org.apache.flink.table.functions.ScalarFunction Maven / Gradle / Ivy
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* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.flink.table.functions;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.InvalidTypesException;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.java.typeutils.TypeExtractor;
import org.apache.flink.table.annotation.DataTypeHint;
import org.apache.flink.table.annotation.FunctionHint;
import org.apache.flink.table.api.ValidationException;
import org.apache.flink.table.catalog.DataTypeFactory;
import org.apache.flink.table.types.extraction.TypeInferenceExtractor;
import org.apache.flink.table.types.inference.TypeInference;
/**
* Base class for a user-defined scalar function. A user-defined scalar function maps zero, one, or
* multiple scalar values to a new scalar value.
*
* The behavior of a {@link ScalarFunction} 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.
*
*
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 {@link
* DataTypeHint} and {@link FunctionHint} annotations.
*
*
The following examples show how to specify a scalar function:
*
*
{@code
* // a function that accepts two INT arguments and computes a sum
* class SumFunction extends ScalarFunction {
* public Integer eval(Integer a, Integer b) {
* return a + b;
* }
* }
*
* // a function that accepts either INT NOT NULL or BOOLEAN NOT NULL and computes a STRING
* class StringifyFunction extends ScalarFunction {
* public String eval(int i) {
* return String.valueOf(i);
* }
* public String eval(boolean b) {
* return String.valueOf(b);
* }
* }
*
* // a function that accepts either INT or BOOLEAN and computes a STRING using function hints
* @FunctionHint(input = [@DataTypeHint("INT")])
* @FunctionHint(input = [@DataTypeHint("BOOLEAN")])
* class StringifyFunction extends ScalarFunction {
* public String eval(Object o) {
* return o.toString();
* }
* }
*
* // a function that accepts any data type as argument and computes a STRING
* class StringifyFunction extends ScalarFunction {
* public String eval(@DataTypeHint(inputGroup = InputGroup.ANY) Object o) {
* return o.toString();
* }
* }
*
* // a function that accepts an arbitrary number of BIGINT values and computes a DECIMAL(10, 4)
* class SumFunction extends ScalarFunction {
* public @DataTypeHint("DECIMAL(10, 4)") BigDecimal eval(Long... values) {
* // ...
* }
* }
* }
*
* For storing a user-defined function in a catalog, the class must have a default constructor
* and must be instantiable during runtime.
*/
@PublicEvolving
public abstract class ScalarFunction extends UserDefinedFunction {
/**
* Returns the result type of the evaluation method with a given signature.
*
* @deprecated This method uses the old type system and is based on the old reflective
* extraction logic. The method will be removed in future versions and is only called when
* using the deprecated {@code TableEnvironment.registerFunction(...)} method. The new
* reflective extraction logic (possibly enriched with {@link DataTypeHint} and {@link
* FunctionHint}) should be powerful enough to cover most use cases. For advanced users, it
* is possible to override {@link UserDefinedFunction#getTypeInference(DataTypeFactory)}.
*/
@Deprecated
public TypeInformation getResultType(Class[] signature) {
return null;
}
/**
* Returns {@link TypeInformation} about the operands of the evaluation method with a given
* signature.
*
* @deprecated This method uses the old type system and is based on the old reflective
* extraction logic. The method will be removed in future versions and is only called when
* using the deprecated {@code TableEnvironment.registerFunction(...)} method. The new
* reflective extraction logic (possibly enriched with {@link DataTypeHint} and {@link
* FunctionHint}) should be powerful enough to cover most use cases. For advanced users, it
* is possible to override {@link UserDefinedFunction#getTypeInference(DataTypeFactory)}.
*/
@Deprecated
public TypeInformation[] getParameterTypes(Class[] signature) {
final TypeInformation[] types = new TypeInformation[signature.length];
for (int i = 0; i < signature.length; i++) {
try {
types[i] = TypeExtractor.getForClass(signature[i]);
} catch (InvalidTypesException e) {
throw new ValidationException(
"Parameter types of scalar function "
+ this.getClass().getCanonicalName()
+ " cannot be automatically determined. Please provide type information manually.");
}
}
return types;
}
@Override
public final FunctionKind getKind() {
return FunctionKind.SCALAR;
}
@Override
public TypeInference getTypeInference(DataTypeFactory typeFactory) {
return TypeInferenceExtractor.forScalarFunction(typeFactory, getClass());
}
}