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Developers/Rust client API/Usage/User-defined functions/Apply a UDF

Apply a UDF

Single record

UDFs that execute on a single record are Record UDFs. The record may or may not exist in the database, which allows the UDF to update or create a record.

To invoke a Record UDF, use Client.execute_udf():

pub fn execute_udf(&self,
 policy: &WritePolicy,
 key: &Key,
 udf_name: &str,
 function_name: &str,
 args: Option<&[Value]>)
 -> Result<Option<Value>>;

Where,

  • policy — The policy governing the operation.
  • key — The key of the record on which to invoke the function.
  • udf_name — The UDF module that contains the function to invoke.
  • function_name — The function to invoke.
  • args — The optional function arguments.

This example defines a UDF in the module examples.lua:

function readBin(r, name)
 return r[name]
end

readBin returns the value of record r in bin name.

The client application can invoke readBin on a record:

let result = client.execute_udf(&WritePolicy::default(),
 &key, "examples", "readBin", as_values!("name"));

key specifies the record to pass to the UDF as the parameter r.

Multiple Arguments

If the UDF accepts multiple arguments, add each argument to client.execute_udf().

For example, if the following UDF is defined in example.lua:

function multiplyAndAdd(r, a, b)
 return r['factor'] * a + b;
end

(This multiplies the bin factor by a and adds b, and returns results to the caller.)

Then, to invoke multiplyAndAdd() from Rust, run:

let result = client.execute_udf(&WritePolicy::default(),
 &key, "examples", "multiplyAndAdd", as_values!(10, 5));
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