Schema/Metadata API Reference: Permissions

The permission layer is designed to restrict the operations that can be performed by various users. Permissions can be defined on various operations (insert/select/update/delete) at a role level granularity. By default, the admin role has unrestricted access to all operations.

Variables in rules

All X-Hasura-* header values can be used in the permission rules. These values can come with the request and can be validated using webhook or can be sent with the JWT token.

create_insert_permission

An insert permission is used to enforce constraints on the data that is being inserted.

Let’s look at an example, a permission for the user role to insert into article table. What is the constraint that we would like to enforce here? A user can only insert articles for themself

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

{
    "type" : "create_insert_permission",
    "args" : {
        "table" : "article",
        "role" : "user",
        "permission" : {
            "check" : {
                "author_id" : "X-HASURA-USER-ID"
            },
            "set":{
                "id":"X-HASURA-USER-ID"
            },
            "columns":["name","author_id"]
        }
    }
}

This reads as follows - For the user role:

  • For every row that is being inserted into the article table, allow insert only if the check passes i.e. that the author_id column value is the same as the value in the request header X-HASURA-USER-ID”.
  • If the above check passes, then access for insert will be limited to columns name and author_id only.
  • When this insert happens, the value of the column id will be automatically set to the value of the resolved session variable X-HASURA-USER-ID.

The argument for check is a boolean expression which has the same syntax as the where clause in the select query, making it extremely expressive. For example,

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

{
    "type" : "create_insert_permission",
    "args" : {
        "table" : "article",
        "role" : "user",
        "permission" : {
            "check" : {
                "author_id" : "X-HASURA-USER-ID",
                "$or" : [
                    {
                        "category" : "editorial",
                        "is_reviewed" : false
                    },
                    {
                        "category" : { "$neq" : "editorial"}
                    }
                ]
            }
        }
    }
}

In the above definition, the row is allowed to be inserted if the author_id is the same as the request’s user id and is_reviewed is false when the category is “editorial”.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role
permission true InsertPermission The permission definition
comment false text comment

InsertPermission

Key Required Schema Description
check true BoolExp This expression has to hold true for every new row that is inserted
set false ColumnPresetsExp Preset values for columns that can sourced from session variables or static values.
columns false PGColumn array (or) '*' Can insert into only these columns (or all when '*' is specified)

drop_insert_permission

Drop an existing insert permission for a role on a table.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role

create_select_permission

A select permission is used to restrict access to only the specified columns and rows.

Let’s look at an example, a permission for the user role to select from article table: all columns can be read, and rows that have been published or authored by themself.

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

{
    "type" : "create_select_permission",
    "args" : {
        "table" : "article",
        "role" : "user",
        "permission" : {
            "columns" : "*",
            "filter" : {
                "$or" : [
                    { "author_id" : "X-HASURA-USER-ID" },
                    { "is_published" : true }
                ]
             },
             "limit": 10,
             "allow_aggregations": true
        }
    }
}

This reads as follows - For the user role:

  • Allow selecting rows where the check passes i.e. is_published is true or the author_id matches the value of the session variable X-HASURA-USER-ID.
  • Allow selecting all columns (because the columns key is set to *).
  • limit the numbers of rows returned by this query to a maximum of 10.
  • Allow aggregate queries.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role
permission true SelectPermission The permission definition
comment false text comment

SelectPermission

Key Required Schema Description
columns true PGColumn array (or) '*' Only these columns are selectable (or all when '*' is specified)
filter true BoolExp Only the rows where this expression holds true are selectable
limit false Integer The maximum number of rows that can be returned
allow_aggregations false Boolean Toggle allowing aggregate queries

drop_select_permission

Drop an existing select permission for a role on a table.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role

create_update_permission

An update permission is used to restrict the columns and rows that can be updated. Its structure is quite similar to the select permission.

An example:

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

{
    "type" : "create_update_permission",
    "args" : {
        "table" : "article",
        "role" : "user",
        "permission" : {
            "columns" : ["title", "content", "category"],
            "filter" : {
                "author_id" : "X-HASURA-USER-ID"
            },
            "set":{
                "id":"X-HASURA-USER-ID"
            }
        }
    }
}

This reads as follows - For the user role:

  • Allow updating only those rows where the check passes i.e. the value of the author_id column of a row matches the value of the session variable X-HASURA-USER-ID value.
  • If the above check passes for a given row, allow updating only the title, content and category columns (as specified in the columns key)
  • When this update happens, the value of the column id will be automatically set to the value of the resolved session variable X-HASURA-USER-ID.

Note

It is important to deny updates to columns that will determine the row ownership. In the above example, author_id column determines the ownership of a row in the article table. Columns such as this should never be allowed to be updated.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role
permission true UpdatePermission The permission definition
comment false text comment

UpdatePermission

Key Required Schema Description
columns true PGColumn array (or) '*' Only these columns are selectable (or all when '*' is specified)
filter true BoolExp Only the rows where this expression holds true are deletable
set false ColumnPresetsExp Preset values for columns that can sourced from session variables or static values.

drop_update_permission

Drop an existing update permission for a role on a table.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role

create_delete_permission

A delete permission is used to restrict the rows that can be deleted.

An example:

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

{
    "type" : "create_delete_permission",
    "args" : {
        "table" : "article",
        "role" : "user",
        "permission" : {
            "filter" : {
                "author_id" : "X-HASURA-USER-ID"
            }
        }
    }
}

This reads as follows:

delete for user role on article table is allowed on rows where author_id is same as the request header X-HASURA-USER-ID value.”

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role
permission true DeletePermission The permission definition
comment false text comment

DeletePermission

Key Required Schema Description
filter true BoolExp Only the rows where this expression holds true are deletable

drop_delete_permission

Drop an existing delete permission for a role on a table.

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName Role

set_permission_comment

set_permission_comment is used to set/update the comment on a permission. Setting the comment to null removes it.

An example:

POST /v1/query HTTP/1.1
Content-Type: application/json
Authorization: Bearer <auth-token> # optional if cookie is set
X-Hasura-Role: admin

{
    "type": "set_permission_comment",
    "args": {
        "table": "article",
        "role": "user",
        "type" : "update",
        "comment" : "can only modify his/her own rows"
    }
}

Args syntax

Key Required Schema Description
table true TableName Name of the table
role true RoleName The role in the permission
type true permission type (one of select/update/delete/insert) The type of the permission
comment false Text comment