org.apache.flink.table.types.logical.utils

Class LogicalTypeCasts

java.lang.Object

org.apache.flink.table.types.logical.utils.LogicalTypeCasts

@Internal
public final class LogicalTypeCasts
extends Object

Utilities for casting LogicalType.

This class aims to be compatible with the SQL standard. It is inspired by Apache Calcite's SqlTypeUtil#canCastFrom method.

Casts can be performed in two ways: implicit or explicit.

Explicit casts correspond to the SQL cast specification and represent the logic behind a CAST(sourceType AS targetType) operation. For example, it allows for converting most types of the LogicalTypeFamily.PREDEFINED family to types of the LogicalTypeFamily.CHARACTER_STRING family.

Implicit casts are used for safe type widening and type generalization (finding a common supertype for a set of types) without loss of information. Implicit casts are similar to the Java semantics (e.g. this is not possible: int x = (String) z).

Conversions that are defined by the LogicalType (e.g. interpreting a DateType as integer value) are not considered here. They are an internal bridging feature that is not standard compliant. If at all, CONVERT methods should make such conversions available.

Method Summary

Modifier and Type	Method and Description
static boolean	supportsAvoidingCast(List<LogicalType> sourceTypes, List<LogicalType> targetTypes) See supportsAvoidingCast(LogicalType, LogicalType).
static boolean	supportsAvoidingCast(LogicalType sourceType, LogicalType targetType) Returns whether the source type can be safely interpreted as the target type.
static boolean	supportsExplicitCast(LogicalType sourceType, LogicalType targetType) Returns whether the source type can be casted to the target type.
static boolean	supportsImplicitCast(LogicalType sourceType, LogicalType targetType) Returns whether the source type can be safely casted to the target type without loosing information.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

supportsAvoidingCast

public static boolean supportsAvoidingCast(LogicalType sourceType,
                                           LogicalType targetType)

Returns whether the source type can be safely interpreted as the target type. This allows avoiding casts by ignoring some logical properties. This is basically a relaxed LogicalType.equals(Object).

In particular this means:

Atomic, non-string types (INT, BOOLEAN, ...) and user-defined structured types must be fully equal (i.e. LogicalType.equals(Object)). However, a NOT NULL type can be stored in NULL type but not vice versa.

Atomic, string types must be contained in the target type (e.g. CHAR(2) is contained in VARCHAR(3), but VARCHAR(2) is not contained in CHAR(3)). Same for binary strings.

Constructed types (ARRAY, ROW, MAP, etc.) and user-defined distinct type must be of same kind but ignore field names and other logical attributes. However, all the children types (LogicalType.getChildren()) must be compatible.

supportsAvoidingCast

public static boolean supportsAvoidingCast(List<LogicalType> sourceTypes,
                                           List<LogicalType> targetTypes)

See supportsAvoidingCast(LogicalType, LogicalType).

supportsImplicitCast

public static boolean supportsImplicitCast(LogicalType sourceType,
                                           LogicalType targetType)

Returns whether the source type can be safely casted to the target type without loosing information.

Implicit casts are used for type widening and type generalization (finding a common supertype for a set of types). Implicit casts are similar to the Java semantics (e.g. this is not possible: int x = (String) z).

supportsExplicitCast

public static boolean supportsExplicitCast(LogicalType sourceType,
                                           LogicalType targetType)

Returns whether the source type can be casted to the target type.

Explicit casts correspond to the SQL cast specification and represent the logic behind a CAST(sourceType AS targetType) operation. For example, it allows for converting most types of the LogicalTypeFamily.PREDEFINED family to types of the LogicalTypeFamily.CHARACTER_STRING family.