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Spring Data Relational support
/*
* Copyright 2022-2023 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.data.relational.core.dialect;
import org.springframework.data.domain.Sort;
/**
* Represents how the {@link Sort.NullHandling} option of an {@code ORDER BY} sort expression is to be evaluated.
*
* @author Chirag Tailor
* @since 2.4
*/
public interface OrderByNullPrecedence {
/**
* An {@link OrderByNullPrecedence} that can be used for databases conforming to the SQL standard which uses
* {@code NULLS FIRST} and {@code NULLS LAST} in {@code ORDER BY} sort expressions to make null values appear before
* or after non-null values in the result set.
*/
OrderByNullPrecedence SQL_STANDARD = new SqlStandardOrderByNullPrecedence();
/**
* An {@link OrderByNullPrecedence} that can be used for databases that do not support the SQL standard usage of
* {@code NULLS FIRST} and {@code NULLS LAST} in {@code ORDER BY} sort expressions to control where null values appear
* respective to non-null values in the result set.
*/
OrderByNullPrecedence NONE = nullHandling -> "";
/**
* Converts a {@link Sort.NullHandling} option to the appropriate SQL text to be included an {@code ORDER BY} sort
* expression.
*/
String evaluate(Sort.NullHandling nullHandling);
/**
* An {@link OrderByNullPrecedence} implementation for databases conforming to the SQL standard which uses
* {@code NULLS FIRST} and {@code NULLS LAST} in {@code ORDER BY} sort expressions to make null values appear before
* or after non-null values in the result set.
*
* @author Chirag Tailor
*/
class SqlStandardOrderByNullPrecedence implements OrderByNullPrecedence {
private static final String NULLS_FIRST = "NULLS FIRST";
private static final String NULLS_LAST = "NULLS LAST";
private static final String UNSPECIFIED = "";
@Override
public String evaluate(Sort.NullHandling nullHandling) {
switch (nullHandling) {
case NULLS_FIRST: return NULLS_FIRST;
case NULLS_LAST: return NULLS_LAST;
case NATIVE: return UNSPECIFIED;
default:
throw new UnsupportedOperationException("Sort.NullHandling " + nullHandling + " not supported");
}
}
}
}