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User-Defined Functions

Enterprise Edition
Couchbase Server 7.0

You can call a user-defined function in any expression where you can call a built-in function.

Description

When you have created a user-defined function, you can call it in any expression, just like a built-in function. User-defined functions have the same syntax as built-in functions, with brackets () to contain any arguments.

The name of the function is usually an unqualified identifier, such as func1 or `func-1`. In this case, the path to the function is determined by the current query context.

To call a global function in a particular namespace, the function name must be a qualified identifier with a namespace, such as default:func1. Similarly, to call a scope function in a particular scope, the function name must be a qualified identifier with the full path to a scope, such as default:`travel-sample`.inventory.func1. Refer to Global Functions and Scope Functions for more details.

The name of a user-defined function is case-sensitive, unlike that of a built-in function. You must call the user-defined function using the same case that was used when it was created.

It is not possible to call a user-defined function in an expression if the function has side effects, such as performing mutations. When you do this, an error is generated.

Arguments

A user-defined function has zero, one, or more arguments, separated by commas, just like a built-in function. Each argument is a N1QL expression required by the function.

If the function was created with named parameters, you must supply all the arguments that were specified when the function was created. If the function was created without named parameters, you cannot supply an argument. If the function is variadic, you can supply as many arguments as needed, or none.

Return Value

The function returns one value, of any valid N1QL type. The result (and the data type of the result) depend on the expression or code that were used to define the function.

If you supply the wrong number of arguments, or arguments with the wrong data type, the possible results differ, depending on whether the function is variadic, or requires a definite number of arguments.

If the function requires a definite number of arguments:

If you do not supply enough arguments, the function generates error 10104: Incorrect number of arguments.
If you supply too many arguments, the function generates error 10104: Incorrect number of arguments.
If any of the arguments have the wrong data type, the function may return unexpected results, depending on the function expression or code.

If the function is variadic:

If you do not supply enough arguments, the function may return unexpected results, depending on the function expression or code.
If you supply too many arguments, the extra parameters are ignored.
If any of the arguments have the wrong data type, the function may return unexpected results, depending on the function expression or code.

Examples

For simplicity, none of these examples implement any data validation or error checking.

(Refer to Inline Functions for details on creating inline user-defined functions.)

Example 1. Inline function with expression

The following statement creates a function called to_meters, which converts feet to meters.

CREATE FUNCTION to_meters(...) { args[0] * 0.3048 };

The following query uses the to_meters function to express the elevation of the selected airports in meters above mean sea level (mamsl). The built-in ROUND function is used to round the output to zero decimal places.

Query

SELECT airportname, ROUND(to_meters(geo.alt)) AS mamsl
FROM `travel-sample`.inventory.airport
LIMIT 5;

Result

[
  {
    "airportname": "Calais Dunkerque",
    "mamsl": 4
  },
  {
    "airportname": "Peronne St Quentin",
    "mamsl": 90
  },
  {
    "airportname": "Les Loges",
    "mamsl": 130
  },
  {
    "airportname": "Couterne",
    "mamsl": 219
  },
  {
    "airportname": "Bray",
    "mamsl": 111
  }
]

Example 2. Inline function with subquery

The following statement creates a function called locations, which selects name and address information from all documents with the specified activity in the landmark keyspace.

CREATE FUNCTION locations(vActivity) { (
  SELECT id, name, address, city
  FROM `travel-sample`.inventory.landmark
  WHERE activity = vActivity) };

The following query uses the locations function as the FROM term in a SELECT query. Compare this query with Example 2 in the section on FROM Subquery.