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Awesome Open Source

EJDB 2.0

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EJDB2 is an embeddable JSON database engine published under MIT license.

The Story of the IT-depression, birds and EJDB 2.0

  • C11 API
  • Single file database
  • Online backups support
  • 500K library size for Android
  • iOS / Android / React Native / Flutter integration
  • Simple but powerful query language (JQL) as well as support of the following standards:
  • Support of collection joins
  • Powered by - The persistent key/value storage engine
  • Provides HTTP REST/Websockets network endpoints with help of
  • JSON documents are stored in using fast and compact binn binary format

EJDB2 platforms matrix

Linux macOS iOS Android Windows
C library ✔️ ✔️ ✔️ ✔️ ✔️1
NodeJS ✔️ ✔️ 3
DartVM ✔️ ✔️2 3
Flutter ✔️ ✔️
React Native 4 ✔️
Swift ✔️ ✔️ ✔️
Java ✔️ ✔️ ✔️ ✔️2

[1] No HTTP/Websocket support #257
[2] Binaries are not distributed with dart pub. You can build it manually
[3] Can be build, but needed a linkage with windows node/dart libs.
[4] Porting in progress #273

Native language bindings

Unofficial EJDB2 language bindings


  • EJDB 2.0 core engine is well tested and used in various heavily loaded deployments
  • Tested on Linux and OSX platforms. Limited Windows support
  • Old EJDB 1.x version can be found in separate ejdb_1.x branch. We are not maintaining ejdb 1.x.

Use cases

Are you using EJDB? Let me know!

macOS / OSX

EJDB2 code ported and tested on High Sierra / Mojave / Catalina

See also EJDB2 Swift binding for OSX, iOS and Linux

brew install ejdb


mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make install



PPA repository

sudo add-apt-repository ppa:adamansky/ejdb2
sudo apt-get update
sudo apt-get install ejdb2

Building debian packages

cmake v3.15 or higher required

mkdir build && cd build
make package

RPM based Linux distributions

mkdir build && cd build
make package


EJDB2 can be cross-compiled for windows

Note: HTTP/Websocket network API is disabled and not supported on Windows until port of library (#257)

Nodejs/Dart bindings not yet ported to Windows.

Cross-compilation Guide for Windows


Sample Android application


EJDB query language (JQL) syntax inspired by ideas behind XPath and Unix shell pipes. It designed for easy querying and updating sets of JSON documents.

JQL grammar

JQL parser created created by peg/leg — recursive-descent parser generators for C Here is the formal parser grammar:

Non formal JQL grammar adapted for brief overview

Notation used below is based on SQL syntax description:

Rule Description
' ' String in single quotes denotes unquoted string literal as part of query.
{ a | b } Curly brackets enclose two or more required alternative choices, separated by vertical bars.
[ ] Square brackets indicate an optional element or clause. Multiple elements or clauses are separated by vertical bars.
| Vertical bars separate two or more alternative syntax elements.
... Ellipses indicate that the preceding element can be repeated. The repetition is unlimited unless otherwise indicated.
( ) Parentheses are grouping symbols.
Unquoted word in lower case Denotes semantic of some query part. For example: placeholder_name - name of any placeholder.

STR = { quoted_string | unquoted_string };

JSONVAL = json_value;

PLACEHOLDER = { ':'placeholder_name | '?' }

FILTERS = FILTER [{ and | or } [ not ] FILTER];

  FILTER = [@collection_name]/NODE[/NODE]...;

  NODE = { '*' | '**' | NODE_EXPRESSION | STR };

                        [{ and | or } [ not ] NODE_EXPRESSION]...;

  OP =   [ '!' ] { '=' | '>=' | '<=' | '>' | '<' | ~ }
      | [ '!' ] { 'eq' | 'gte' | 'lte' | 'gt' | 'lt' }
      | [ not ] { 'in' | 'ni' | 're' };

  NODE_EXPR_LEFT = { '*' | '**' | STR | NODE_KEY_EXPR };



APPLY = { 'apply' | 'upsert' } { PLACEHOLDER | json_object | json_array  } | 'del'

OPTS = { 'skip' n | 'limit' n | 'count' | 'noidx' | 'inverse' | ORDERBY }...

  ORDERBY = { 'asc' | 'desc' } PLACEHOLDER | json_path


  PROJECTION = 'all' | json_path

  • json_value: Any valid JSON value: object, array, string, bool, number.
  • json_path: Simplified JSON pointer. Eg.: /foo/bar or /foo/"bar with spaces"/
  • * in context of NODE: Any JSON object key name at particular nesting level.
  • ** in context of NODE: Any JSON object key name at arbitrary nesting level.
  • * in context of NODE_EXPR_LEFT: Key name at specific level.
  • ** in context of NODE_EXPR_LEFT: Nested array value of array element under specific key.

JQL quick introduction

Lets play with some very basic data and queries. For simplicity we will use ejdb websocket network API which provides us a kind of interactive CLI. The same job can be done using pure C API too (ejdb2.h jql.h).

NOTE: Take a look into JQL test cases for more examples.

  "firstName": "John",
  "lastName": "Doe",
  "age": 28,
  "pets": [
    {"name": "Rexy rex", "kind": "dog", "likes": ["bones", "jumping", "toys"]},
    {"name": "Grenny", "kind": "parrot", "likes": ["green color", "night", "toys"]}

Save json as sample.json then upload it the family collection:

# Start HTTP/WS server protected by some access token
./jbs -a 'myaccess01'
8 Mar 16:15:58.601 INFO: HTTP/WS endpoint at localhost:9191

Server can be accessed using HTTP or Websocket endpoint. More info

curl -d '@sample.json' -H'X-Access-Token:myaccess01' -X POST http://localhost:9191/family

We can play around using interactive wscat websocket client.

wscat  -H 'X-Access-Token:myaccess01' -c http://localhost:9191
connected (press CTRL+C to quit)
> k info
< k     {
 "version": "2.0.0",
 "file": "db.jb",
 "size": 8192,
 "collections": [
   "name": "family",
   "dbid": 3,
   "rnum": 1,
   "indexes": []

> k get family 1
< k     1       {
 "firstName": "John",
 "lastName": "Doe",
 "age": 28,
 "pets": [
   "name": "Rexy rex",
   "kind": "dog",
   "likes": [
   "name": "Grenny",
   "kind": "parrot",
   "likes": [
    "green color",

Note about the k prefix before every command; It is an arbitrary key chosen by client and designated to identify particular websocket request, this key will be returned with response to request and allows client to identify that response for his particular request. More info

Query command over websocket has the following format:

<key> query <collection> <query>

So we will consider only <query> part in this document.

Get all elements in collection

k query family /*


k query family /**

or specify collection name in query explicitly

k @family/*

We can execute query by HTTP POST request

curl --data-raw '@family/[firstName = John]' -H'X-Access-Token:myaccess01' -X POST http://localhost:9191

1	{"firstName":"John","lastName":"Doe","age":28,"pets":[{"name":"Rexy rex","kind":"dog","likes":["bones","jumping","toys"]},{"name":"Grenny","kind":"parrot","likes":["green color","night","toys"]}]}

Set the maximum number of elements in result set

k @family/* | limit 10

Get documents where specified json path exists

Element at index 1 exists in likes array within a pets sub-object

> k query family /pets/*/likes/1
< k     1       {"firstName":"John"...

Element at index 1 exists in likes array at any likes nesting level

> k query family /**/likes/1
< k     1       {"firstName":"John"...

From this point and below I will omit websocket specific prefix k query family and consider only JQL queries.

Get documents by primary key

In order to get documents by primary key the following options are available:

  1. Use API call ejdb_get()

     const doc = await db.get('users', 112);
  2. Use the special query construction: /=:? or @collection/=:?

Get document from users collection with primary key 112

> k @users/=112

Update tags array for document in jobs collection (TypeScript):

 await db.createQuery('@jobs/ = :? | apply :? | count')
    .setNumber(0, id)
    .setJSON(1, { tags })

Array of primary keys can also be used for matching:

 await db.createQuery('@jobs/ = :?| apply :? | count')
    .setJSON(0, [23, 1, 2])
    .setJSON(1, { tags })

Matching JSON entry values

Below is a set of self explaining queries:

/pets/*/[name = "Rexy rex"]

/pets/*/[name eq "Rexy rex"]

/pets/*/[name = "Rexy rex" or name = Grenny]

Note about quotes around words with spaces.

Get all documents where owner age greater than 20 and have some pet who like bones or toys

/[age > 20] and /pets/*/likes/[** in ["bones", "toys"]]

Here ** denotes some element in likes array.

ni is the inverse operator to in. Get documents where bones somewhere in likes array.

/pets/*/[likes ni "bones"]

We can create more complicated filters

( /[age <= 20] or /[lastName re "Do.*"] )
  and /pets/*/likes/[** in ["bones", "toys"]]

Note about grouping parentheses and regular expression matching using re operator.

~ is a prefix matching operator (Since ejdb v2.0.53). Prefix matching can benefit from using indexes.

Get documents where /lastName starts with "Do".

/[lastName ~ Do]

Arrays and maps can be matched as is

Filter documents with likes array exactly matched to ["bones","jumping","toys"]

/**/[likes = ["bones","jumping","toys"]]

Matching algorithms for arrays and maps are different:

  • Array elements are matched from start to end. In equal arrays all values at the same index should be equal.
  • Object maps matching consists of the following steps:
    • Lexicographically sort object keys in both maps.
    • Do matching keys and its values starting from the lowest key.
    • If all corresponding keys and values in one map are fully matched to ones in other and vice versa, maps considered to be equal. For example: {"f":"d","e":"j"} and {"e":"j","f":"d"} are equal maps.

Conditions on key names

Find JSON document having firstName key at root level.

/[* = "firstName"]

I this context * denotes a key name.

You can use conditions on key name and key value at the same time:

/[[* = "firstName"] = John]

Key name can be either firstName or lastName but should have John value in any case.

/[[* in ["firstName", "lastName"]] = John]

It may be useful in queries with dynamic placeholders (C API):

/[[* = :keyName] = :keyValue]

JQL data modification

APPLY section responsible for modification of documents content.

APPLY = ({'apply' | `upsert`} { PLACEHOLDER | json_object | json_array  }) | 'del'

JSON patch specs conformed to rfc7386 or rfc6902 specifications followed after apply keyword.

Let's add address object to all matched document

/[firstName = John] | apply {"address":{"city":"New York", "street":""}}

If JSON object is an argument of apply section it will be treated as merge match (rfc7386) otherwise it should be array which denotes rfc6902 JSON patch. Placeholders also supported by apply section.

/* | apply :?

Set the street name in address

/[firstName = John] | apply [{"op":"replace", "path":"/address/street", "value":"Fifth Avenue"}]

Add Neo fish to the set of John's pets

/[firstName = John]
| apply [{"op":"add", "path":"/pets/-", "value": {"name":"Neo", "kind":"fish"}}]

upsert updates existing document by given json argument used as merge patch or inserts provided json argument as new document instance.

/[firstName = John] | upsert {"firstName": "John", "address":{"city":"New York"}}

Non standard JSON patch extensions


Increments numeric value identified by JSON path by specified value.


 Document:  {"foo": 1}
 Patch:     [{"op": "increment", "path": "/foo", "value": 2}]
 Result:    {"foo": 3}


Same as JSON patch add but creates intermediate object nodes for missing JSON path segments.


Document: {"foo": {"bar": 1}}
Patch:    [{"op": "add_create", "path": "/foo/zaz/gaz", "value": 22}]
Result:   {"foo":{"bar":1,"zaz":{"gaz":22}}}


Document: {"foo": {"bar": 1}}
Patch:    [{"op": "add_create", "path": "/foo/bar/gaz", "value": 22}]
Result:   Error since element pointed by /foo/bar is not an object


Swaps two values of JSON document starting from from path.

Swapping rules

  1. If value pointed by from not exists error will be raised.
  2. If value pointed by path not exists it will be set by value from from path, then object pointed by from path will be removed.
  3. If both values pointed by from and path are presented they will be swapped.


Document: {"foo": ["bar"], "baz": {"gaz": 11}}
Patch:    [{"op": "swap", "from": "/foo/0", "path": "/baz/gaz"}]
Result:   {"foo": [11], "baz": {"gaz": "bar"}}

Example (Demo of rule 2):

Document: {"foo": ["bar"], "baz": {"gaz": 11}}
Patch:    [{"op": "swap", "from": "/foo/0", "path": "/baz/zaz"}]
Result:   {"foo":[],"baz":{"gaz":11,"zaz":"bar"}}

Removing documents

Use del keyword to remove matched elements from collection:

/FILTERS | del


> k add family {"firstName":"Jack"}
< k     2
> k query family /[firstName re "Ja.*"]
< k     2       {"firstName":"Jack"}

# Remove selected elements from collection
> k query family /[firstName=Jack] | del
< k     2       {"firstName":"Jack"}

JQL projections


  PROJECTION = 'all' | json_path | join_clause

Projection allows to get only subset of JSON document excluding not needed data.

Lets add one more document to our collection:

$ cat << EOF | curl -d @- -H'X-Access-Token:myaccess01' -X POST http://localhost:9191/family
"pets":[{"name":"Sonic", "kind":"mouse", "likes":[]}]

Now query only pet owners firstName and lastName from collection.

> k query family /* | /{firstName,lastName}

< k     3       {"firstName":"Jack","lastName":"Parker"}
< k     1       {"firstName":"John","lastName":"Doe"}
< k

Add pets array for every document

> k query family /* | /{firstName,lastName} + /pets

< k     3       {"firstName":"Jack","lastName":"Parker","pets":[...
< k     1       {"firstName":"John","lastName":"Doe","pets":[...

Exclude only pets field from documents

> k query family /* | all - /pets

< k     3       {"firstName":"Jack","lastName":"Parker","age":35}
< k     1       {"firstName":"John","lastName":"Doe","age":28,"address":{"city":"New York","street":"Fifth Avenue"}}
< k

Here all keyword used denoting whole document.

Get age and the first pet in pets array.

> k query family /[age > 20] | /age + /pets/0

< k     3       {"age":35,"pets":[{"name":"Sonic","kind":"mouse","likes":[]}]}
< k     1       {"age":28,"pets":[{"name":"Rexy rex","kind":"dog","likes":["bones","jumping","toys"]}]}
< k

JQL collection joins

Join materializes reference to document to a real document objects which will replace reference inplace.

Documents are joined by their primary keys only.

Reference keys should be stored in referrer document as number or string field.

Joins can be specified as part of projection expression in the following form:



  • field ‐ JSON field contains primary key of joined document.
  • < ‐ The special mark symbol which instructs EJDB engine to replace field key by body of joined document.
  • collection ‐ name of DB collection where joined documents located.

A referrer document will be untouched if associated document is not found.

Here is the simple demonstration of collection joins in our interactive websocket shell:

> k add artists {"name":"Leonardo Da Vinci", "years":[1452,1519]}
< k     1
> k add paintings {"name":"Mona Lisa", "year":1490, "origin":"Italy", "artist": 1}
< k     1
> k add paintings {"name":"Madonna Litta - Madonna And The Child", "year":1490, "origin":"Italy", "artist": 1}
< k     2

# Lists paintings documents

> k @paintings/*
< k     2       {"name":"Madonna Litta - Madonna And The Child","year":1490,"origin":"Italy","artist":1}
< k     1       {"name":"Mona Lisa","year":1490,"origin":"Italy","artist":1}
< k

# Do simple join with artists collection

> k @paintings/* | /artist<artists
< k     2       {"name":"Madonna Litta - Madonna And The Child","year":1490,"origin":"Italy",
                  "artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}

< k     1       {"name":"Mona Lisa","year":1490,"origin":"Italy",
                  "artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k

# Strip all document fields except `name` and `artist` join

> k @paintings/* | /artist<artists + /name + /artist/*
< k     2       {"name":"Madonna Litta - Madonna And The Child","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k     1       {"name":"Mona Lisa","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k

# Same results as above:

> k @paintings/* | /{name, artist<artists} + /artist/*
< k     2       {"name":"Madonna Litta - Madonna And The Child","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k     1       {"name":"Mona Lisa","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k

Invalid references:

>  k add paintings {"name":"Mona Lisa2", "year":1490, "origin":"Italy", "artist": 9999}
< k     3
> k @paintings/* |  /artist<artists
< k     3       {"name":"Mona Lisa2","year":1490,"origin":"Italy","artist":9999}
< k     2       {"name":"Madonna Litta - Madonna And The Child","year":1490,"origin":"Italy","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}
< k     1       {"name":"Mona Lisa","year":1490,"origin":"Italy","artist":{"name":"Leonardo Da Vinci","years":[1452,1519]}}

JQL results ordering

  ORDERBY = ({ 'asc' | 'desc' } PLACEHOLDER | json_path)...

Lets add one more document then sort documents in collection according to firstName ascending and age descending order.

> k add family {"firstName":"John", "lastName":"Ryan", "age":39}
< k     4
> k query family /* | /{firstName,lastName,age} | asc /firstName desc /age
< k     3       {"firstName":"Jack","lastName":"Parker","age":35}
< k     4       {"firstName":"John","lastName":"Ryan","age":39}
< k     1       {"firstName":"John","lastName":"Doe","age":28}
< k

asc, desc instructions may use indexes defined for collection to avoid a separate documents sorting stage.

JQL Options

OPTS = { 'skip' n | 'limit' n | 'count' | 'noidx' | 'inverse' | ORDERBY }...
  • skip n Skip first n records before first element in result set
  • limit n Set max number of documents in result set
  • count Returns only count of matched documents
    > k query family /* | count
    < k     3
    < k
  • noidx Do not use any indexes for query execution.
  • inverse By default query scans documents from most recently added to older ones. This option inverts scan direction to opposite and activates noidx mode. Has no effect if query has asc/desc sorting clauses.

JQL Indexes and performance tips

Database index can be build for any JSON field path containing values of number or string type. Index can be an unique ‐ not allowing value duplication and non unique. The following index mode bit mask flags are used (defined in ejdb2.h):

Index mode Description
0x01 EJDB_IDX_UNIQUE Index is unique
0x04 EJDB_IDX_STR Index for JSON string field value type
0x08 EJDB_IDX_I64 Index for 8 bytes width signed integer field values
0x10 EJDB_IDX_F64 Index for 8 bytes width signed floating point field values.

For example unique index of string type will be specified by EJDB_IDX_UNIQUE | EJDB_IDX_STR = 0x05. Index can be defined for only one value type located under specific path in json document.

Lets define non unique string index for /lastName path:

> k idx family 4 /lastName
< k

Index selection for queries based on set of heuristic rules.

You can always check index usage by issuing explain command in WS API:

> k explain family /[lastName=Doe] and /[age!=27]
< k     explain [INDEX] MATCHED  STR|3 /lastName EXPR1: 'lastName = Doe' INIT: IWKV_CURSOR_EQ

The following statements are taken into account when using EJDB2 indexes:

  • Only one index can be used for particular query execution

  • If query consist of or joined part at top level or contains negated expressions at the top level of query expression - indexes will not be in use at all. So no indexes below:

    /[lastName != Andy]
    /[lastName = "John"] or /[lastName = Peter]

    But will be used /lastName index defined above

    /[lastName = Doe]
    /[lastName = Doe] and /[age = 28]
    /[lastName = Doe] and not /[age = 28]
    /[lastName = Doe] and /[age != 28]
  • The following operators are supported by indexes (ejdb 2.0.x):

    • eq, =
    • gt, >
    • gte, >=
    • lt, <
    • lte, <=
    • in
    • ~ (Prefix matching since ejdb 2.0.53)
  • ORDERBY clauses may use indexes to avoid result set sorting.

  • Array fields can also be indexed. Let's outline typical use case: indexing of some entity tags:

    > k add books {"name":"Mastering Ultra", "tags":["ultra", "language", "bestseller"]}
    < k     1
    > k add books {"name":"Learn something in 24 hours", "tags":["bestseller"]}
    < k     2
    > k query books /*
    < k     2       {"name":"Learn something in 24 hours","tags":["bestseller"]}
    < k     1       {"name":"Mastering Ultra","tags":["ultra","language","bestseller"]}
    < k

    Create string index for /tags

    > k idx books 4 /tags
    < k

    Filter books by bestseller tag and show index usage in query:

    > k explain books /tags/[** in ["bestseller"]]
    < k     explain [INDEX] MATCHED  STR|4 /tags EXPR1: '** in ["bestseller"]' INIT: IWKV_CURSOR_EQ
    [INDEX] SELECTED STR|4 /tags EXPR1: '** in ["bestseller"]' INIT: IWKV_CURSOR_EQ
    < k     1       {"name":"Mastering Ultra","tags":["ultra","language","bestseller"]}
    < k     2       {"name":"Learn something in 24 hours","tags":["bestseller"]}
    < k

Performance tip: Physical ordering of documents

All documents in collection are sorted by their primary key in descending order. So if you use auto generated keys (ejdb_put_new) you may be sure what documents fetched as result of full scan query will be ordered according to the time of insertion in descendant order, unless you don't use query sorting, indexes or inverse keyword.

Performance tip: Brute force scan vs indexed access

In many cases, using index may drop down the overall query performance. Because index collection contains only document references (id) and engine may perform an addition document fetching by its primary key to finish query matching. So for not so large collections a brute scan may perform better than scan using indexes. However, exact matching operations: eq, in and sorting by natural index order will benefit from index in most cases.

Performance tip: Get rid of unnecessary document data

If you'd like update some set of documents with apply or del operations but don't want fetching all of them as result of query - just add count modifier to the query to get rid of unnecessary data transferring and json data conversion.

HTTP REST/Websocket API endpoint

EJDB engine provides the ability to start a separate HTTP/Websocket endpoint worker exposing network API for quering and data modifications.

The easiest way to expose database over the network is using the standalone jbs server. (Of course if you plan to avoid C API integration).

jbs server

jbs -h

EJDB 2.0.0 standalone REST/Websocket server.

 --file <>	Database file path. Default: db.jb
 -f <>    	(same as --file)
 --port ##	HTTP port number listen to. Default: 9191
 -p ##    	(same as --port)
 --bind <>	Address server listen. Default: localhost
 -b <>    	(same as --bind)
 --access <>	Server access token matched to 'X-Access-Token' HTTP header value
 -a <>      	(same as --access)
 --trunc   	Cleanup existing database file on open
 -t        	(same as --trunc)
 --wal   	Use write ahead logging (WAL). Must be set for data durability.
 -w      	(same as --wal)

Advanced options
 --sbz ##	Max sorting buffer size. If exceeded, an overflow temp file for data will be created. Default: 16777216, min: 1048576
 --dsz ##	Initial size of buffer to process/store document on queries. Preferable average size of document. Default: 65536, min: 16384
 --bsz ##	Max HTTP/WS API document body size. Default: 67108864, min: 524288

Use any of the following input formats:
	-arg <value>	-arg=<value>	-arg<value>

Use the -h, -help or -? to get this information again.


Access to HTTP endpoint can be protected by a token specified with --access command flag or by C API EJDB_HTTP options. If access token specified on server, client must provide X-Access-Token HTTP header value. If token is required and not provided by client the 401 HTTP code will be reported. If access token is not matched to the token provided the 403 HTTP code will be returned. For any other errors server will respond with 500 error code.


POST /{collection}

Add a new document to the collection.

  • 200 success. Body: a new document identifier as int64 number

PUT /{collection}/{id}

Replaces/store document under specific numeric id

  • 200 on success. Empty body

DELETE /{collection}/{id}

Removes document identified by id from a collection

  • 200 on success. Empty body
  • 404 if document not found

PATCH /{collection}/{id}

Patch a document identified by id by rfc7396, rfc6902 data.

  • 200 on success. Empty body

GET | HEAD /{collections}/{id}

Retrieve document identified by id from a collection.

  • 200 on success. Body: JSON document text.
    • content-type:application/json
    • content-length:
  • 404 if document not found


Query a collection by provided query as POST body. Body of query should contains collection name in use in the first filter element: @collection_name/... Request headers:

  • X-Hints comma separated extra hints to ejdb2 database engine.
    • explain Show query execution plan before first element in result set separated by -------------------- line. Response:
  • Response data transfered using HTTP chunked transfer encoding
  • 200 on success.
  • JSON documents separated by \n in the following format:
    \r\n<document id>\t<document JSON body>


curl -v --data-raw '@family/[age > 18]' -H 'X-Access-Token:myaccess01' http://localhost:9191
* Rebuilt URL to: http://localhost:9191/
*   Trying
* Connected to localhost ( port 9191 (#0)
> POST / HTTP/1.1
> Host: localhost:9191
> User-Agent: curl/7.58.0
> Accept: */*
> X-Access-Token:myaccess01
> Content-Length: 18
> Content-Type: application/x-www-form-urlencoded
* upload completely sent off: 18 out of 18 bytes
< HTTP/1.1 200 OK
< connection:keep-alive
< content-type:application/json
< transfer-encoding:chunked

4	{"firstName":"John","lastName":"Ryan","age":39}
3	{"firstName":"Jack","lastName":"Parker","age":35,"pets":[{"name":"Sonic","kind":"mouse","likes":[]}]}
1	{"firstName":"John","lastName":"Doe","age":28,"pets":[{"name":"Rexy rex","kind":"dog","likes":["bones","jumping","toys"]},{"name":"Grenny","kind":"parrot","likes":["green color","night","toys"]}],"address":{"city":"New York","street":"Fifth Avenue"}}
* Connection #0 to host localhost left intact
curl --data-raw '@family/[lastName = "Ryan"]' -H 'X-Access-Token:myaccess01' -H 'X-Hints:explain' http://localhost:9191
[INDEX] MATCHED  STR|3 /lastName EXPR1: 'lastName = "Ryan"' INIT: IWKV_CURSOR_EQ
[INDEX] SELECTED STR|3 /lastName EXPR1: 'lastName = "Ryan"' INIT: IWKV_CURSOR_EQ
4	{"firstName":"John","lastName":"Ryan","age":39}


Fetch ejdb JSON metadata and available HTTP methods in Allow response header. Example:

curl -X OPTIONS -H 'X-Access-Token:myaccess01'  http://localhost:9191/
 "version": "2.0.0",
 "file": "db.jb",
 "size": 16384,
 "collections": [
   "name": "family",
   "dbid": 3,
   "rnum": 3,
   "indexes": [
     "ptr": "/lastName",
     "mode": 4,
     "idbf": 64,
     "dbid": 4,
     "rnum": 3

Websocket API

EJDB supports simple text based protocol over HTTP websocket protocol. You can use interactive websocket CLI tool wscat to communicate with server by hands.



Will respond with the following help text message:

wscat  -H 'X-Access-Token:myaccess01' -c http://localhost:9191
> ?
<key> info
<key> get     <collection> <id>
<key> set     <collection> <id> <document json>
<key> add     <collection> <document json>
<key> del     <collection> <id>
<key> patch   <collection> <id> <patch json>
<key> idx     <collection> <mode> <path>
<key> rmi     <collection> <mode> <path>
<key> rmc     <collection>
<key> query   <collection> <query>
<key> explain <collection> <query>
<key> <query>

Note about <key> prefix before every command; It is an arbitrary key chosen by client and designated to identify particular websocket request, this key will be returned with response to request and allows client to identify that response for his particular request.

Errors are returned in the following format:

<key> ERROR: <error description>

<key> info

Get database metadatas as JSON document.

<key> get <collection> <id>

Retrieve document identified by id from a collection. If document is not found IWKV_ERROR_NOTFOUND will be returned.


> k get family 3
< k     3       {
 "firstName": "Jack",
 "lastName": "Parker",
 "age": 35,
 "pets": [
   "name": "Sonic",
   "kind": "mouse",
   "likes": []

If document not found we will get error:

> k get family 55
< k ERROR: Key not found. (IWKV_ERROR_NOTFOUND)

<key> set <collection> <id> <document json>

Replaces/add document under specific numeric id. Collection will be created automatically if not exists.

<key> add <collection> <document json>

Add new document to <collection> New id of document will be generated and returned as response. `Collection> will be created automatically if not exists.


> k add mycollection {"foo":"bar"}
< k     1
> k add mycollection {"foo":"bar"}
< k     2

<key> del <collection> <id>

Remove document identified by id from the collection. If document is not found IWKV_ERROR_NOTFOUND will be returned.

<key> patch <collection> <id> <patch json>

Apply rfc7396 or rfc6902 patch to the document identified by id. If document is not found IWKV_ERROR_NOTFOUND will be returned.

<key> query <collection> <query>

Execute query on documents in specified collection. Response: A set of WS messages with document boidies terminated by the last message with empty body.

> k query family /* | /firstName
< k     4       {"firstName":"John"}
< k     3       {"firstName":"Jack"}
< k     1       {"firstName":"John"}
< k

Note about last message: <key> with no body.

<key> explain <collection> <query>

Same as <key> query <collection> <query> but the first response message will be prefixed by <key> explain and contains query execution plan.


> k explain family /* | /firstName
< k     explain [INDEX] NO [COLLECTOR] PLAIN

< k     4       {"firstName":"John"}
< k     3       {"firstName":"Jack"}
< k     1       {"firstName":"John"}
< k

Execute query text. Body of query should contains collection name in use in the first filter element: @collection_name/.... Behavior is the same as for: <key> query <collection> <query>

<key> idx <collection> <mode> <path>

Ensure index with specified mode (bitmask flag) for given json path and collection. Collection will be created if not exists.

Index mode Description
0x01 EJDB_IDX_UNIQUE Index is unique
0x04 EJDB_IDX_STR Index for JSON string field value type
0x08 EJDB_IDX_I64 Index for 8 bytes width signed integer field values
0x10 EJDB_IDX_F64 Index for 8 bytes width signed floating point field values.

Set unique string index (0x01 & 0x04) = 5 on /name JSON field:

k idx mycollection 5 /name

<key> rmi <collection> <mode> <path>

Remove index with specified mode (bitmask flag) for given json path and collection. Return error if given index not found.

<key> rmc <collection>

Remove collection and all of its data. Note: If collection is not found no errors will be reported.

Docker support

If you have Docker installed, you can build a Docker image and run it in a container

cd docker
docker build -t ejdb2 .
docker run -d -p 9191:9191 --name myEJDB ejdb2 --access myAccessKey

or get an image of ejdb2 directly from the Docker Hub

docker run -d -p 9191:9191 --name myEJDB softmotions/ejdb2 --access myAccessKey


EJDB can be embedded into any C/C++ application. C API documented in the following headers:

  • ejdb.h Main API functions
  • jbl.h JSON documents management API
  • jql.h Query building API

Example application:

#include <ejdb2/ejdb2.h>

#define CHECK(rc_)          \
  if (rc_) {                 \
    iwlog_ecode_error3(rc_); \
    return 1;                \

static iwrc documents_visitor(EJDB_EXEC *ctx, const EJDB_DOC doc, int64_t *step) {
  // Print document to stderr
  return jbl_as_json(doc->raw, jbl_fstream_json_printer, stderr, JBL_PRINT_PRETTY);

int main() {

  EJDB_OPTS opts = {
    .kv = {
      .path = "example.db",
      .oflags = IWKV_TRUNC
  EJDB db;     // EJDB2 storage handle
  int64_t id;  // Document id placeholder
  JQL q = 0;   // Query instance
  JBL jbl = 0; // Json document

  iwrc rc = ejdb_init();

  rc = ejdb_open(&opts, &db);

  // First record
  rc = jbl_from_json(&jbl, "{\"name\":\"Bianca\", \"age\":4}");
  RCGO(rc, finish);
  rc = ejdb_put_new(db, "parrots", jbl, &id);
  RCGO(rc, finish);

  // Second record
  rc = jbl_from_json(&jbl, "{\"name\":\"Darko\", \"age\":8}");
  RCGO(rc, finish);
  rc = ejdb_put_new(db, "parrots", jbl, &id);
  RCGO(rc, finish);

  // Now execute a query
  rc =  jql_create(&q, "parrots", "/[age > :age]");
  RCGO(rc, finish);

  EJDB_EXEC ux = {
    .db = db,
    .q = q,
    .visitor = documents_visitor

  // Set query placeholder value.
  // Actual query will be /[age > 3]
  rc = jql_set_i64(q, "age", 0, 3);
  RCGO(rc, finish);

  // Now execute the query
  rc = ejdb_exec(&ux);

  return 0;

Compile and run:

gcc -std=gnu11 -Wall -pedantic -c -o example1.o example1.c
gcc -o example1 example1.o -lejdb2

 "name": "Darko",
 "age": 8
 "name": "Bianca",
 "age": 4


MIT License

Copyright (c) 2012-2021 Softmotions Ltd <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.


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