custom-functions.mdx

sidebar_label	sidebar_position	description	keywords
Custom functions	3	Manage custom functions with the Hasura Metadata API	hasura docs Metadata API API reference custom function

Metadata API Reference: Custom Functions

Introduction

Track/untrack a custom SQL function in the Hasura GraphQL Engine.

Only tracked custom functions are available for querying/mutating/subscribing data over the GraphQL API.

:::tip Supported from

The Metadata API is supported for versions v2.0.0 and above and replaces the older schema/Metadata API.

:::

pg_track_function {#metadata-pg-track-function}

pg_track_function is used to add a custom SQL function to the GraphQL schema. It supports more configuration options than v1, and also supports tracking custom functions as mutations. Also refer a note here.

Track an SQL function called search_articles with a Hasura session argument:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type": "pg_track_function",
    "args": {
        "source": "default",
        "function": {
            "schema": "public",
            "name": "search_articles"
        },
        "configuration": {
            "session_argument": "hasura_session"
        },
        "comment": "This function helps search for articles"
    }
}

Track VOLATILE SQL function reset_widget as a mutation, so it appears as a top-level field under the mutation root field:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type": "pg_track_function",
    "args": {
        "function": {
            "schema": "public",
            "name": "reset_widget"
        },
        "configuration": {
            "exposed_as": "mutation"
        },
        "source": "default"
    }
}

If exposed_as is omitted, the location in the schema to expose the function will be inferred from the function's volatility, with VOLATILE functions appearing under the mutation root, and others ending up under query/subscription.

In most cases you will want VOLATILE functions to only be exposed as mutations, and only STABLE and IMMUTABLE functions to be queries. When tracking VOLATILE functions under the query root, the user needs to guarantee that the field is idempotent and side-effect free, in the context of the resulting GraphQL API.

One such use case might be a function that wraps a simple query and performs some logging visible only to administrators.

:::info Note

It's easy to accidentally give an SQL function the wrong volatility (or for a function to end up with VOLATILE mistakenly, since it's the default).

:::

Args syntax {#metadata-pg-track-function-syntax}

Key	Required	Schema	Description
function	true	FunctionName	Name of the SQL function
configuration	false	Function Configuration	Configuration for the SQL function
source	false	SourceName	Name of the source database of the function (default: default)
comment	false	String	Comment for the function. This comment would replace the auto-generated comment for the function field in the GraphQL schema.

pg_untrack_function {#metadata-pg-untrack-function}

pg_untrack_function is used to remove a SQL function from the GraphQL schema.

Remove an SQL function search_articles:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type": "pg_untrack_function",
    "args": {
        "function": {
           "schema": "public",
           "name": "search_articles"
        },
        "source": "default"
    }
}

Args syntax {#metadata-pg-untrack-function-syntax}

Key	Required	Schema	Description
function	true	FunctionName	Name of the SQL function
source	false	SourceName	Name of the source database of the function (default: default)

pg_set_function_customization {#metadata-pg-set-function-customization}

pg_set_function_customization allows you to customize any given function with a custom name and custom root fields of an already tracked function. This will replace the already present customization.

Set the configuration for a function called search_articles:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
   "type": "pg_set_function_customization",
   "args": {
     "function": "search_articles",
     "source": "default",
     "configuration": {
       "custom_root_fields": {
         "function": "FindArticles",
         "function_aggregate": "FindArticlesAgg"
       }
     }
   }
}

Args syntax {#metadata-pg-set-function-customization-syntax}

Key	Required	Schema	Description
function	true	FunctionName	Name of the function
configuration	false	Function Configuration	Configuration for the function
source	false	SourceName	Name of the source database of the function (default: default)

pg_create_function_permission {#metadata-pg-create-function-permission}

pg_create_function_permission is used to add permission to an existing custom function. To add a function permission, the provided role should have select permissions to the target table of the function.

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type": "pg_create_function_permission",
    "args": {
       "function": "get_articles",
       "source": "default",
       "role": "user"
    }
}

Args syntax {#metadata-pg-create-function-permission-syntax}

Key	Required	Schema	Description
function	true	FunctionName	Name of the SQL function
role	true	RoleName	Name of the role
source	false	Text	Name of the source database of the function (default: default)

pg_drop_function_permission {#metadata-pg-drop-function-permission}

pg_drop_function_permission is used to drop an existing function permission.

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
    "type": "pg_drop_function_permission",
    "args": {
       "function": "get_articles",
       "role": "user",
       "source": "default"
    }
}

Args syntax {#metadata-pg-drop-function-permission-syntax}

Key	Required	Schema	Description
function	true	FunctionName	Name of the SQL function
role	true	RoleName	Name of the role
source	false	Text	Name of the source database of the function (default: default)