@PublicEvolving public class AsyncScalarFunction extends UserDefinedFunction
The behavior of a AsyncScalarFunction
can be defined by implementing a custom
evaluation method. An evaluation method must be declared publicly and named eval
.
Evaluation methods can also be overloaded by implementing multiple methods named eval
. The first argument of the method must be a CompletableFuture
of the return type. The method body must complete the
future either if there is a result or if it completes exceptionally.
By default, input and output data types are automatically extracted using reflection. If the
reflective information is not sufficient, it can be supported and enriched with DataTypeHint
and FunctionHint
annotations.
The following examples show how to specify an async scalar function:
// a function that accepts two INT arguments and computes a sum class SumFunction extends AsyncScalarFunction { public void eval(CompletableFuturefuture, Integer a, Integer b) { return future.complete(a + b); } } // a function that accepts either INT NOT NULL or BOOLEAN NOT NULL and computes a STRING class StringifyFunction extends AsyncScalarFunction { public void eval(CompletableFuture future, int i) { return future.complete(String.valueOf(i)); } public void eval(CompletableFuture future, boolean b) { return future.complete(String.valueOf(b)); } } // a function that accepts either INT or BOOLEAN and computes a STRING using function hints
Constructor and Description |
---|
AsyncScalarFunction() |
Modifier and Type | Method and Description |
---|---|
FunctionKind |
getKind()
Returns the kind of function this definition describes.
|
TypeInference |
getTypeInference(DataTypeFactory typeFactory)
Returns the logic for performing type inference of a call to this function definition.
|
close, functionIdentifier, open, toString
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
getRequirements, isDeterministic
public final FunctionKind getKind()
FunctionDefinition
public TypeInference getTypeInference(DataTypeFactory typeFactory)
UserDefinedFunction
The type inference process is responsible for inferring unknown types of input arguments, validating input arguments, and producing result types. The type inference process happens independent of a function body. The output of the type inference is used to search for a corresponding runtime implementation.
Instances of type inference can be created by using TypeInference.newBuilder()
.
See BuiltInFunctionDefinitions
for concrete usage examples.
The type inference for user-defined functions is automatically extracted using reflection.
It does this by analyzing implementation methods such as eval() or accumulate()
and
the generic parameters of a function class if present. If the reflective information is not
sufficient, it can be supported and enriched with DataTypeHint
and FunctionHint
annotations.
Note: Overriding this method is only recommended for advanced users. If a custom type inference is specified, it is the responsibility of the implementer to make sure that the output of the type inference process matches with the implementation method:
The implementation method must comply with each DataType.getConversionClass()
returned by the type inference. For example, if DataTypes.TIMESTAMP(3).bridgedTo(java.sql.Timestamp.class)
is an expected argument type, the
method must accept a call eval(java.sql.Timestamp)
.
Regular Java calling semantics (including type widening and autoboxing) are applied when
calling an implementation method which means that the signature can be eval(java.lang.Object)
.
The runtime will take care of converting the data to the data format specified by the
DataType.getConversionClass()
coming from the type inference logic.
getTypeInference
in interface FunctionDefinition
getTypeInference
in class UserDefinedFunction
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