EJDB 2.0

Build Status Join Telegram license maintained

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 iowow.io - The persistent key/value storage engine
  • Provides HTTP REST/Websockets network endpoints with help of facil.io
  • 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 Native 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 http://facil.io 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: https://github.com/Softmotions/ejdb/blob/master/src/jql/jqp.leg

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' -q -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

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

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npm install ejdb2_react_native
yarn add ejdb2_react_native




  • Softmotions