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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8c2f8e8 · 2026-10-19

Moduleesqueleto-3.6.0.3Haskell2010

Database.Esqueleto.PostgreSQL.JSON

This module contains PostgreSQL-specific JSON functions.

A couple of things to keep in mind about this module:

  • The Type column in the PostgreSQL documentation tables are the types of the right operand, the left is always jsonb.

  • Since these operators can all take NULL values as their input, and most can also output NULL values (even when the inputs are guaranteed to not be NULL), all JSONB values are wrapped in Maybe. This also makes it easier to chain them. (cf. JSONBExpr) Just use the just function to lift any non-Maybe JSONB values in case it doesn't type check.

  • As long as the previous operator's resulting value is a JSONBExpr, any other JSON operator can be used to transform the JSON further. (e.g. [1,2,3] -> 1 @> 2)

The PostgreSQL version the functions work with are included in their description.

  • 3 types
  • 14 values

JSONB Newtype

3 declarations

With JSONB, you can use your Haskell types in your database table models as long as your type has FromJSON and ToJSON instances.

import Database.Persist.TH

share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistUpperCase|
  Example
    json (JSONB MyType)
|]

CAUTION: Remember that changing the FromJSON instance of your type might result in old data becoming unparsable! You can use (JSONB Data.Aeson.Value) for unstructured/variable JSON.

newtypenewtype JSONB a
#

Newtype wrapper around any type with a JSON representation.

Constructors

Instances13Functor, Foldable, Traversable, Eq, Ord, Read, …
  • Functor JSONBDefined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Foldable JSONBDefined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Traversable JSONBDefined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Eq a => Eq (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Ord a => Ord (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Read a => Read (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Show a => Show (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • Generic (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • FromJSON a => FromJSON (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • ToJSON a => ToJSON (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • (FromJSON a, ToJSON a) => PersistField (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances
  • (FromJSON a, ToJSON a) => PersistFieldSql (JSONB a)Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances

    jsonb

  • type Rep (JSONB a) = D1 ('MetaData "JSONB" "Database.Esqueleto.PostgreSQL.JSON.Instances" "esqueleto-3.6.0.3-KVpHHG85upIAWWc7HlRkE8" 'True) (C1 ('MetaCons "JSONB" 'PrefixI 'True) (S1 ('MetaSel ('Just "unJSONB") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))Defined in esqueleto-3.6.0.3 · Database.Esqueleto.PostgreSQL.JSON.Instances

JSONAccessor

1 declaration
datadata JSONAccessor
#

Used with certain JSON operators.

This data type has Num and IsString instances for ease of use by using integer and string literals.

Example2 expressions
3 :: JSONAccessorJSONIndex 3-3 :: JSONAccessorJSONIndex -3
Example1 expression
"name" :: JSONAccessorJSONKey "name"

NOTE: DO NOT USE ANY OF THE Num METHODS ON THIS TYPE!

Constructors

Instances6Eq, Num, Show, IsString, Generic, Rep

Arrow operators

4 declarations

Better documentation included with individual functions

The arrow operators are selection functions to select values from JSON arrays or objects.

PostgreSQL Documentation

Requires PostgreSQL version >= 9.3

     | Type   | Description                                |  Example                                         | Example Result
-----+--------+--------------------------------------------+--------------------------------------------------+----------------
 ->  | int    | Get JSON array element (indexed from zero, | '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 | {"c":"baz"}
     |        | negative integers count from the end)      |                                                  |
 ->  | text   | Get JSON object field by key               | '{"a": {"b":"foo"}}'::json->a                  | {"b":"foo"}
 ->> | int    | Get JSON array element as text             | '[1,2,3]'::json->>2                              | 3
 ->> | text   | Get JSON object field as text              | '{"a":1,"b":2}'::json->>b                      | 2
 #>  | text[] | Get JSON object at specified path          | '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}'       | {"c": "foo"}
 #>> | text[] | Get JSON object at specified path as text  | '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}'      | 3
value(->.) :: JSONBExpr a -> JSONAccessor -> JSONBExpr b
#

Requires PostgreSQL version >= 9.3

This function extracts the jsonb value from a JSON array or object, depending on whether you use an int or a text. (cf. JSONAccessor)

As long as the left operand is jsonb, this function will not throw an exception, but will return NULL when an int is used on anything other than a JSON array, or a text is used on anything other than a JSON object.

PostgreSQL Documentation
    | Type | Description                                |  Example                                         | Example Result
----+------+--------------------------------------------+--------------------------------------------------+----------------
 -> | int  | Get JSON array element (indexed from zero) | '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 | {"c":"baz"}
 -> | text | Get JSON object field by key               | '{"a": {"b":"foo"}}'::json->a                  | {"b":"foo"}
value(->>.) :: JSONBExpr a -> JSONAccessor -> SqlExpr (Value (Maybe Text))
#

Requires PostgreSQL version >= 9.3

Identical to ->., but the resulting DB type is a text, so it could be chained with anything that uses text.

CAUTION: if the "scalar" JSON value null is the result of this function, PostgreSQL will interpret it as a PostgreSQL NULL value, and will therefore be Nothing instead of (Just "null")

PostgreSQL Documentation
     | Type | Description                    |  Example                    | Example Result
-----+------+--------------------------------+-----------------------------+----------------
 ->> | int  | Get JSON array element as text | '[1,2,3]'::json->>2         | 3
 ->> | text | Get JSON object field as text  | '{"a":1,"b":2}'::json->>b | 2
value(#>.) :: JSONBExpr a -> [Text] -> JSONBExpr b
#

Requires PostgreSQL version >= 9.3

This operator can be used to select a JSON value from deep inside another one. It only works on objects and arrays and will result in NULL (Nothing) when encountering any other JSON type.

The Texts used in the right operand list will always select an object field, but can also select an index from a JSON array if that text is parsable as an integer.

Consider the following:

x ^. TestBody #>. ["0","1"]

The following JSON values in the test table's body column will be affected:

 Values in column                     | Resulting value
--------------------------------------+----------------------------
{"0":{"1":"Got it!"}}                 | "Got it!"
{"0":[null,["Got it!","Even here!"]]} | ["Got it!", "Even here!"]
[{"1":"Got it again!"}]               | "Got it again!"
[[null,{"Wow":"so deep!"}]]           | {"Wow": "so deep!"}
false                                 | NULL
"nope"                                | NULL
3.14                                  | NULL
PostgreSQL Documentation
     | Type   | Description                       |  Example                                   | Example Result
-----+--------+-----------------------------------+--------------------------------------------+----------------
 #>  | text[] | Get JSON object at specified path | '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}' | {"c": "foo"}
value(#>>.) :: JSONBExpr a -> [Text] -> SqlExpr (Value (Maybe Text))
#

Requires PostgreSQL version >= 9.3

This function is to #>. as ->>. is to ->.

CAUTION: if the "scalar" JSON value null is the result of this function, PostgreSQL will interpret it as a PostgreSQL NULL value, and will therefore be Nothing instead of (Just "null")

PostgreSQL Documentation
     | Type   | Description                               |  Example                                    | Example Result
-----+--------+-------------------------------------------+---------------------------------------------+----------------
 #>> | text[] | Get JSON object at specified path as text | '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' | 3

Filter operators

5 declarations

Better documentation included with individual functions

These functions test certain properties of JSON values and return booleans, so are mainly used in WHERE clauses.

PostgreSQL Documentation

Requires PostgreSQL version >= 9.4

    | Type   | Description                                                     |  Example
----+--------+-----------------------------------------------------------------+---------------------------------------------------
 @> | jsonb  | Does the left JSON value contain within it the right value?     | '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb
 <@ | jsonb  | Is the left JSON value contained within the right value?        | '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb
 ?  | text   | Does the string exist as a top-level key within the JSON value? | '{"a":1, "b":2}'::jsonb ? b
 ?| | text[] | Do any of these array strings exist as top-level keys?          | '{"a":1, "b":2, "c":3}'::jsonb ?| array[b, c]
 ?& | text[] | Do all of these array strings exist as top-level keys?          | '["a", "b"]'::jsonb ?& array[a, b]
value(@>.) :: JSONBExpr a -> JSONBExpr b -> SqlExpr (Value Bool)
#

Requires PostgreSQL version >= 9.4

This operator checks for the JSON value on the right to be a subset of the JSON value on the left.

Examples of the usage of this operator can be found in the Database.Persist.Postgresql.JSON module.

(here: https://hackage.haskell.org/package/persistent-postgresql-2.10.0/docs/Database-Persist-Postgresql-JSON.html)

PostgreSQL Documentation
    | Type  | Description                                                 |  Example
----+-------+-------------------------------------------------------------+---------------------------------------------
 @> | jsonb | Does the left JSON value contain within it the right value? | '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb
value(<@.) :: JSONBExpr a -> JSONBExpr b -> SqlExpr (Value Bool)
#

Requires PostgreSQL version >= 9.4

This operator works the same as @>., just with the arguments flipped. So it checks for the JSON value on the left to be a subset of JSON value on the right.

Examples of the usage of this operator can be found in the Database.Persist.Postgresql.JSON module.

(here: https://hackage.haskell.org/package/persistent-postgresql-2.10.0/docs/Database-Persist-Postgresql-JSON.html)

PostgreSQL Documentation
    | Type  | Description                                              |  Example
----+-------+----------------------------------------------------------+---------------------------------------------
 <@ | jsonb | Is the left JSON value contained within the right value? | '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb
value(?.) :: JSONBExpr a -> Text -> SqlExpr (Value Bool)
#

Requires PostgreSQL version >= 9.4

This operator checks if the given text is a top-level member of the JSON value on the left. This means a top-level field in an object, a top-level string in an array or just a string value.

Examples of the usage of this operator can be found in the Database.Persist.Postgresql.JSON module.

(here: https://hackage.haskell.org/package/persistent-postgresql-2.10.0/docs/Database-Persist-Postgresql-JSON.html)

PostgreSQL Documentation
   | Type | Description                                                     |  Example
---+------+-----------------------------------------------------------------+-------------------------------
 ? | text | Does the string exist as a top-level key within the JSON value? | '{"a":1, "b":2}'::jsonb ? b
value(?|.) :: JSONBExpr a -> [Text] -> SqlExpr (Value Bool)
#

Requires PostgreSQL version >= 9.4

This operator checks if ANY of the given texts is a top-level member of the JSON value on the left. This means any top-level field in an object, any top-level string in an array or just a string value.

Examples of the usage of this operator can be found in the Database.Persist.Postgresql.JSON module.

(here: https://hackage.haskell.org/package/persistent-postgresql-2.10.0/docs/Database-Persist-Postgresql-JSON.html)

PostgreSQL Documentation
    | Type   | Description                                            |  Example
----+--------+--------------------------------------------------------+---------------------------------------------------
 ?| | text[] | Do any of these array strings exist as top-level keys? | '{"a":1, "b":2, "c":3}'::jsonb ?| array[b, c]
value(?&.) :: JSONBExpr a -> [Text] -> SqlExpr (Value Bool)
#

Requires PostgreSQL version >= 9.4

This operator checks if ALL of the given texts are top-level members of the JSON value on the left. This means a top-level field in an object, a top-level string in an array or just a string value.

Examples of the usage of this operator can be found in the Database.Persist.Postgresql.JSON module.

(here: https://hackage.haskell.org/package/persistent-postgresql-2.10.0/docs/Database-Persist-Postgresql-JSON.html)

PostgreSQL Documentation
    | Type   | Description                                            |  Example
----+--------+--------------------------------------------------------+----------------------------------------
 ?& | text[] | Do all of these array strings exist as top-level keys? | '["a", "b"]'::jsonb ?& array[a, b]

Deletion and concatenation operators

4 declarations

Better documentation included with individual functions

These operators change the shape of the JSON value and also have the highest risk of throwing an exception. Please read the descriptions carefully before using these functions.

PostgreSQL Documentation

Requires PostgreSQL version >= 9.5

    | Type    | Description                                                            |  Example
----+---------+------------------------------------------------------------------------+-------------------------------------------------
 || | jsonb   | Concatenate two jsonb values into a new jsonb value                    | '["a", "b"]'::jsonb || '["c", "d"]'::jsonb
 -  | text    | Delete key/value pair or string element from left operand.             | '{"a": "b"}'::jsonb - a
    |         | Key/value pairs are matched based on their key value.                  |
 -  | integer | Delete the array element with specified index (Negative integers count | '["a", "b"]'::jsonb - 1
    |         | from the end). Throws an error if top level container is not an array. |
 #- | text[]  | Delete the field or element with specified path                        | '["a", {"b":1}]'::jsonb #- '{1,b}'
    |         | (for JSON arrays, negative integers count from the end)                |

Requires PostgreSQL version >= 10

    | Type    | Description                                                            |  Example
----+---------+------------------------------------------------------------------------+-------------------------------------------------
 -  | text[]  | Delete multiple key/value pairs or string elements from left operand.  | '{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[]
    |         | Key/value pairs are matched based on their key value.                  |
value(-.) :: JSONBExpr a -> JSONAccessor -> JSONBExpr b
#

Requires PostgreSQL version >= 9.5

This operator can remove a key from an object or a string element from an array when using text, and remove certain elements by index from an array when using integers.

Negative integers delete counting from the end of the array. (e.g. -1 being the last element, -2 being the second to last, etc.)

CAUTION: THIS FUNCTION THROWS AN EXCEPTION WHEN USED ON ANYTHING OTHER THAN OBJECTS OR ARRAYS WHEN USING TEXT, AND ANYTHING OTHER THAN ARRAYS WHEN USING INTEGERS!

Objects and arrays
{"a": 3.14}            - "a"         == {}
{"a": "b"}             - "b"         == {"a": "b"}
{"a": 3.14}            - "a"         == {}
{"a": 3.14, "c": true} - "a"         == {"c": true}
["a", 2, "c"]          - "a"         == [2, "c"] -- can remove strings from arrays
[true, "b", 5]         - 0           == ["b", 5]
[true, "b", 5]         - 3           == [true, "b", 5]
[true, "b", 5]         - -1          == [true, "b"]
[true, "b", 5]         - -4          == [true, "b", 5]
[]                     - 1           == []
{"1": true}            - 1           == ERROR: cannot delete from object using integer index
1                      - <anything>  == ERROR: cannot delete from scalar
"a"                    - <anything>  == ERROR: cannot delete from scalar
true                   - <anything>  == ERROR: cannot delete from scalar
null                   - <anything>  == ERROR: cannot delete from scalar
PostgreSQL Documentation
   | Type    | Description                                                            |  Example
---+---------+------------------------------------------------------------------------+-------------------------------------------------
 - | text    | Delete key/value pair or string element from left operand.             | '{"a": "b"}'::jsonb - a
   |         | Key/value pairs are matched based on their key value.                  |
 - | integer | Delete the array element with specified index (Negative integers count | '["a", "b"]'::jsonb - 1
   |         | from the end). Throws an error if top level container is not an array. |
value(--.) :: JSONBExpr a -> [Text] -> JSONBExpr b
#

Requires PostgreSQL version >= 10

Removes a set of keys from an object, or string elements from an array.

This is the same operator internally as -., but the option to use a text array, instead of text or integer was only added in version 10. That's why this function is seperate from -.

NOTE: The following is equivalent:

{some JSON expression} -. "a" -. "b"

is equivalent to

{some JSON expression} --. ["a","b"]
PostgreSQL Documentation
   | Type    | Description                                                            |  Example
---+---------+------------------------------------------------------------------------+-------------------------------------------------
 - | text[]  | Delete multiple key/value pairs or string elements from left operand.  | '{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[]
   |         | Key/value pairs are matched based on their key value.                  |
value(#-.) :: JSONBExpr a -> [Text] -> JSONBExpr b
#

Requires PostgreSQL version >= 9.5

This operator can remove elements nested in an object.

If a Text is not parsable as a number when selecting in an array (even when halfway through the selection) an exception will be thrown.

Negative integers delete counting from the end of an array. (e.g. -1 being the last element, -2 being the second to last, etc.)

CAUTION: THIS FUNCTION THROWS AN EXCEPTION WHEN USED ON ANYTHING OTHER THAN OBJECTS OR ARRAYS, AND WILL ALSO THROW WHEN TRYING TO SELECT AN ARRAY ELEMENT WITH A NON-INTEGER TEXT

Objects
{"a": 3.14, "b": null}        #- []        == {"a": 3.14, "b": null}
{"a": 3.14, "b": null}        #- ["a"]     == {"b": null}
{"a": 3.14, "b": null}        #- ["a","b"] == {"a": 3.14, "b": null}
{"a": {"b":false}, "b": null} #- ["a","b"] == {"a": {}, "b": null}
Arrays
[true, {"b":null}, 5]       #- []            == [true, {"b":null}, 5]
[true, {"b":null}, 5]       #- ["0"]         == [{"b":null}, 5]
[true, {"b":null}, 5]       #- ["b"]         == ERROR: path element at position 1 is not an integer: "b"
[true, {"b":null}, 5]       #- ["1","b"]     == [true, {}, 5]
[true, {"b":null}, 5]       #- ["-2","b"]    == [true, {}, 5]
{"a": {"b":[false,4,null]}} #- ["a","b","2"] == {"a": {"b":[false,4]}}
{"a": {"b":[false,4,null]}} #- ["a","b","c"] == ERROR: path element at position 3 is not an integer: "c"
Other values
1    #- {anything} == ERROR: cannot delete from scalar
"a"  #- {anything} == ERROR: cannot delete from scalar
true #- {anything} == ERROR: cannot delete from scalar
null #- {anything} == ERROR: cannot delete from scalar
PostgreSQL Documentation
    | Type   | Description                                             |  Example
----+--------+---------------------------------------------------------+------------------------------------
 #- | text[] | Delete the field or element with specified path         | '["a", {"b":1}]'::jsonb #- '{1,b}'
    |        | (for JSON arrays, negative integers count from the end) |
value(||.) :: JSONBExpr a -> JSONBExpr b -> JSONBExpr c
#

Requires PostgreSQL version >= 9.5

This operator concatenates two JSON values. The behaviour is self-evident when used on two arrays, but the behaviour on different combinations of JSON values might behave unexpectedly.

CAUTION: THIS FUNCTION THROWS AN EXCEPTION WHEN CONCATENATING A JSON OBJECT WITH A JSON SCALAR VALUE!

Arrays

This operator is a standard concatenation function when used on arrays:

[1,2]   || [2,3]   == [1,2,2,3]
[]      || [1,2,3] == [1,2,3]
[1,2,3] || []      == [1,2,3]
Objects

When concatenating JSON objects with other JSON objects, the fields from the JSON object on the right are added to the JSON object on the left. When concatenating a JSON object with a JSON array, the object will be inserted into the array; either on the left or right, depending on the position relative to the operator.

When concatening an object with a scalar value, an exception is thrown.

{"a": 3.14}                    || {"b": true}         == {"a": 3.14, "b": true}
{"a": "b"}                     || {"a": null}         == {"a": null}
{"a": {"b": true, "c": false}} || {"a": {"b": false}} == {"a": {"b": false}}
{"a": 3.14}                    || [1,null]            == [{"a": 3.14},1,null]
[1,null]                       || {"a": 3.14}         == [1,null,{"a": 3.14}]
1                              || {"a": 3.14}         == ERROR: invalid concatenation of jsonb objects
{"a": 3.14}                    || false               == ERROR: invalid concatenation of jsonb objects
Scalar values

Scalar values can be thought of as being singleton arrays when used with this operator. This rule does not apply when concatenating with JSON objects.

1          || null       == [1,null]
true       || "a"        == [true,"a"]
[1,2]      || false      == [1,2,false]
null       || [1,"a"]    == [null,1,"a"]
{"a":3.14} || true       == ERROR: invalid concatenation of jsonb objects
3.14       || {"a":3.14} == ERROR: invalid concatenation of jsonb objects
{"a":3.14} || [true]     == [{"a":3.14},true]
[false]    || {"a":3.14} == [false,{"a":3.14}]
PostgreSQL Documentation
    | Type  | Description                                         |  Example
----+-------+-----------------------------------------------------+--------------------------------------------
 || | jsonb | Concatenate two jsonb values into a new jsonb value | '["a", "b"]'::jsonb || '["c", "d"]'::jsonb

Note: The || operator concatenates the elements at the top level of each of its operands. It does not operate recursively.

For example, if both operands are objects with a common key field name, the value of the field in the result will just be the value from the right hand operand.