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MongoDB support for Spring Data
/*
* Copyright 2017-2020 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.mongodb.core.aggregation;
import org.bson.Document;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
/**
* Encapsulates the aggregation framework {@code $sortByCount}-operation.
*
* {@code $sortByCount} stage is typically used with {@link Aggregation} and {@code $facet}. Groups incoming documents
* based on the value of a specified expression and computes the count of documents in each distinct group.
* {@link SortByCountOperation} is equivalent to {@code { $group: { _id: , count: { $sum: 1 } } }, { $sort:
* { count: -1 } }}.
*
* We recommend to use the static factory method {@link Aggregation#sortByCount(String)} instead of creating instances
* of this class directly.
*
* @see https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/
* @author Jérôme Guyon
* @author Mark Paluch
* @since 2.1
*/
public class SortByCountOperation implements AggregationOperation {
private final @Nullable Field groupByField;
private final @Nullable AggregationExpression groupByExpression;
/**
* Creates a new {@link SortByCountOperation} given a {@link Field group-by field}.
*
* @param groupByField must not be {@literal null}.
*/
public SortByCountOperation(Field groupByField) {
Assert.notNull(groupByField, "Group by field must not be null!");
this.groupByField = groupByField;
this.groupByExpression = null;
}
/**
* Creates a new {@link SortByCountOperation} given a {@link AggregationExpression group-by expression}.
*
* @param groupByExpression must not be {@literal null}.
*/
public SortByCountOperation(AggregationExpression groupByExpression) {
Assert.notNull(groupByExpression, "Group by expression must not be null!");
this.groupByExpression = groupByExpression;
this.groupByField = null;
}
/*
* (non-Javadoc)
* @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDocument(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
*/
@Override
public Document toDocument(AggregationOperationContext context) {
return new Document(getOperator(), groupByExpression == null ? context.getReference(groupByField).toString()
: groupByExpression.toDocument(context));
}
/*
* (non-Javadoc)
* @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
*/
@Override
public String getOperator() {
return "$sortByCount";
}
}