Allow to estimate document count.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>3.4.0-SNAPSHOT</version>
+	<version>3.4.0-GH-3522-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.4.0-SNAPSHOT</version>
+		<version>3.4.0-GH-3522-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-distribution/pom.xml

@@ -14,7 +14,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.4.0-SNAPSHOT</version>
+		<version>3.4.0-GH-3522-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -11,7 +11,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.4.0-SNAPSHOT</version>
+		<version>3.4.0-GH-3522-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoOperations.java

@@ -1179,8 +1179,11 @@ <S, T> T findAndReplace(Query query, S replacement, FindAndReplaceOptions option
 	 *          {@literal null}.
 	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
 	 * @return the count of matching documents.
+	 * @since 3.4
 	 */
-	long count(Query query, Class<?> entityClass);
+	default long exactCount(Query query, Class<?> entityClass) {
+		return exactCount(query, entityClass, getCollectionName(entityClass));
+	}
 
 	/**
 	 * Returns the number of documents for the given {@link Query} querying the given collection. The given {@link Query}
@@ -1201,6 +1204,71 @@ <S, T> T findAndReplace(Query query, S replacement, FindAndReplaceOptions option
 	 * @param collectionName must not be {@literal null} or empty.
 	 * @return the count of matching documents.
 	 * @see #count(Query, Class, String)
+	 * @since 3.4
+	 */
+	default long exactCount(Query query, String collectionName) {
+		return exactCount(query, null, collectionName);
+	}
+
+	/**
+	 * Returns the number of documents for the given {@link Query} by querying the given collection using the given entity
+	 * class to map the given {@link Query}. <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(String)} for empty queries instead.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
+	 *          {@literal null}.
+	 * @param entityClass the parametrized type. Can be {@literal null}.
+	 * @param collectionName must not be {@literal null} or empty.
+	 * @return the count of matching documents.
+	 * @since 3.4
+	 */
+	long exactCount(Query query, @Nullable Class<?> entityClass, String collectionName);
+
+	/**
+	 * Returns the number of documents for the given {@link Query} by querying the collection of the given entity class.
+	 * <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} which may have an impact on performance.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
+	 *          {@literal null}.
+	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
+	 * @return the count of matching documents.
+	 */
+	long count(Query query, Class<?> entityClass);
+
+	/**
+	 * Returns the number of documents for the given {@link Query} querying the given collection. The given {@link Query}
+	 * must solely consist of document field references as we lack type information to map potential property references
+	 * onto document fields. Use {@link #count(Query, Class, String)} to get full type specific support. <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} which may have an impact on performance.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents.
+	 * @param collectionName must not be {@literal null} or empty.
+	 * @return the count of matching documents.
+	 * @see #count(Query, Class, String)
 	 */
 	long count(Query query, String collectionName);
 
@@ -1241,11 +1309,9 @@ default long estimatedCount(Class<?> entityClass) {
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
 	 * <br />
-	 * This method uses an
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
 	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
-	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
-	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
-	 * {@link #estimatedCount(String)} for empty queries instead.
+	 * aggregation execution} which may have an impact on performance.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
 	 *          {@literal null}.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -22,13 +22,13 @@
 import java.math.RoundingMode;
 import java.util.*;
 import java.util.concurrent.TimeUnit;
+import java.util.function.BiPredicate;
 import java.util.stream.Collectors;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.bson.Document;
 import org.bson.conversions.Bson;
-
 import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -188,6 +188,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 	private SessionSynchronization sessionSynchronization = SessionSynchronization.ON_ACTUAL_TRANSACTION;
 
+	private CountExecution countExecution = this::doExactCount;
+
 	/**
 	 * Constructor used for a basic template configuration.
 	 *
@@ -345,6 +347,47 @@ public void setEntityCallbacks(EntityCallbacks entityCallbacks) {
 		this.entityCallbacks = entityCallbacks;
 	}
 
+	/**
+	 * En-/Disable usage of estimated count.
+	 *
+	 * @param enabled if {@literal true} {@link MongoCollection#estimatedDocumentCount()} ()} will we used for unpaged,
+	 *          empty {@link Query queries}.
+	 * @since 3.4
+	 */
+	public void useEstimatedCount(boolean enabled) {
+		useEstimatedCount(enabled, this::countCanBeEstimated);
+	}
+
+	/**
+	 * En-/Disable usage of estimated count based on the given {@link BiPredicate estimationFilter}.
+	 *
+	 * @param enabled if {@literal true} {@link MongoCollection#estimatedDocumentCount()} will we used for {@link Document
+	 *          filter queries} that pass the given {@link BiPredicate estimationFilter}.
+	 * @param estimationFilter the {@link BiPredicate filter}.
+	 * @since 3.4
+	 */
+	private void useEstimatedCount(boolean enabled, BiPredicate<Document, CountOptions> estimationFilter) {
+
+		if (enabled) {
+
+			this.countExecution = (collectionName, filter, options) -> {
+
+				if (!estimationFilter.test(filter, options)) {
+					return doExactCount(collectionName, filter, options);
+				}
+
+				EstimatedDocumentCountOptions estimatedDocumentCountOptions = new EstimatedDocumentCountOptions();
+				if (options.getMaxTime(TimeUnit.MILLISECONDS) > 0) {
+					estimatedDocumentCountOptions.maxTime(options.getMaxTime(TimeUnit.MILLISECONDS), TimeUnit.MILLISECONDS);
+				}
+
+				return doEstimatedCount(collectionName, estimatedDocumentCountOptions);
+			};
+		} else {
+			this.countExecution = this::doExactCount;
+		}
+	}
+
 	/**
 	 * Inspects the given {@link ApplicationContext} for {@link MongoPersistentEntityIndexCreator} and those in turn if
 	 * they were registered for the current {@link MappingContext}. If no creator for the current {@link MappingContext}
@@ -1106,6 +1149,17 @@ public long count(Query query, String collectionName) {
 		return count(query, null, collectionName);
 	}
 
+	@Override
+	public long exactCount(Query query, @Nullable Class<?> entityClass, String collectionName) {
+
+		CountContext countContext = queryOperations.countQueryContext(query);
+
+		CountOptions options = countContext.getCountOptions(entityClass);
+		Document mappedQuery = countContext.getMappedQuery(entityClass, mappingContext::getPersistentEntity);
+
+		return doExactCount(collectionName, mappedQuery, options);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.MongoOperations#count(org.springframework.data.mongodb.core.query.Query, java.lang.Class, java.lang.String)
@@ -1131,10 +1185,29 @@ protected long doCount(String collectionName, Document filter, CountOptions opti
 					.debug(String.format("Executing count: %s in collection: %s", serializeToJsonSafely(filter), collectionName));
 		}
 
+		return countExecution.countDocuments(collectionName, filter, options);
+	}
+
+	protected long doExactCount(String collectionName, Document filter, CountOptions options) {
 		return execute(collectionName,
 				collection -> collection.countDocuments(CountQuery.of(filter).toQueryDocument(), options));
 	}
 
+	protected boolean countCanBeEstimated(Document filter, CountOptions options) {
+
+		return
+		// only empty filter for estimatedCount
+		filter.isEmpty() &&
+		// no skip, no limit,...
+				isEmptyOptions(options) &&
+				// transaction active?
+				!MongoDatabaseUtils.isTransactionActive(getMongoDatabaseFactory());
+	}
+
+	private boolean isEmptyOptions(CountOptions options) {
+		return options.getLimit() <= 0 && options.getSkip() <= 0;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.MongoOperations#estimatedCount(java.lang.String)
@@ -3571,5 +3644,15 @@ public MongoDatabase getDb() {
 			// native MongoDB objects that offer methods with ClientSession must not be proxied.
 			return delegate.getDb();
 		}
+
+		@Override
+		protected boolean countCanBeEstimated(Document filter, CountOptions options) {
+			return false;
+		}
+	}
+
+	@FunctionalInterface
+	interface CountExecution {
+		long countDocuments(String collection, Document filter, CountOptions options);
 	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoOperations.java

@@ -951,8 +951,11 @@ <S, T> Mono<T> findAndReplace(Query query, S replacement, FindAndReplaceOptions
 	 *          {@literal null}.
 	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
 	 * @return the count of matching documents.
+	 * @since 3.4
 	 */
-	Mono<Long> count(Query query, Class<?> entityClass);
+	default Mono<Long> exactCount(Query query, Class<?> entityClass) {
+		return exactCount(query, entityClass, getCollectionName(entityClass));
+	}
 
 	/**
 	 * Returns the number of documents for the given {@link Query} querying the given collection. The given {@link Query}
@@ -973,8 +976,11 @@ <S, T> Mono<T> findAndReplace(Query query, S replacement, FindAndReplaceOptions
 	 * @param collectionName must not be {@literal null} or empty.
 	 * @return the count of matching documents.
 	 * @see #count(Query, Class, String)
+	 * @since 3.4
 	 */
-	Mono<Long> count(Query query, String collectionName);
+	default Mono<Long> exactCount(Query query, String collectionName) {
+		return exactCount(query, null, collectionName);
+	}
 
 	/**
 	 * Returns the number of documents for the given {@link Query} by querying the given collection using the given entity
@@ -995,6 +1001,66 @@ <S, T> Mono<T> findAndReplace(Query query, S replacement, FindAndReplaceOptions
 	 * @param entityClass the parametrized type. Can be {@literal null}.
 	 * @param collectionName must not be {@literal null} or empty.
 	 * @return the count of matching documents.
+	 * @since 3.4
+	 */
+	Mono<Long> exactCount(Query query, @Nullable Class<?> entityClass, String collectionName);
+
+	/**
+	 * Returns the number of documents for the given {@link Query} by querying the collection of the given entity class.
+	 * <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} which may have an impact on performance.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
+	 *          {@literal null}.
+	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
+	 * @return the count of matching documents.
+	 */
+	Mono<Long> count(Query query, Class<?> entityClass);
+
+	/**
+	 * Returns the number of documents for the given {@link Query} querying the given collection. The given {@link Query}
+	 * must solely consist of document field references as we lack type information to map potential property references
+	 * onto document fields. Use {@link #count(Query, Class, String)} to get full type specific support. <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} which may have an impact on performance.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents.
+	 * @param collectionName must not be {@literal null} or empty.
+	 * @return the count of matching documents.
+	 * @see #count(Query, Class, String)
+	 */
+	Mono<Long> count(Query query, String collectionName);
+
+	/**
+	 * Returns the number of documents for the given {@link Query} by querying the given collection using the given entity
+	 * class to map the given {@link Query}. <br />
+	 * <strong>NOTE:</strong> Query {@link Query#getSkip() offset} and {@link Query#getLimit() limit} can have direct
+	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
+	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
+	 * count all matches.
+	 * <br />
+	 * This method may choose to use {@link #estimatedCount(Class)} for empty queries instead of running an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} which may have an impact on performance.
+	 *
+	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
+	 *          {@literal null}.
+	 * @param entityClass the parametrized type. Can be {@literal null}.
+	 * @param collectionName must not be {@literal null} or empty.
+	 * @return the count of matching documents.
 	 */
 	Mono<Long> count(Query query, @Nullable Class<?> entityClass, String collectionName);