Add support for reactive cursor windowing.

Author: mp911de

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

@@ -15,13 +15,24 @@
  */
 package org.springframework.data.mongodb.core;
 
+import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 
+import org.bson.Document;
 import org.springframework.data.domain.CursorRequest;
 import org.springframework.data.domain.CursorWindow;
+import org.springframework.data.domain.KeysetCursorRequest;
+import org.springframework.data.domain.Sort;
+import org.springframework.data.domain.Sort.Order;
+import org.springframework.data.mongodb.core.EntityOperations.Entity;
+import org.springframework.data.mongodb.core.query.Query;
 
 /**
+ * Utilities to run cursor window queries and create cursor window results.
+ *
  * @author Mark Paluch
+ * @since 4.1
  */
 class CursorUtils {
 
@@ -42,7 +53,104 @@ static <T> List<T> getSubList(CursorRequest request, List<T> result) {
 		return result;
 	}
 
-	public static <T> CursorWindow<T> createWindow(CursorRequest cursorRequest, List<T> result) {
+	/**
+	 * Create the actual query to run keyset-based pagination. Affects projection, sorting, and the criteria.
+	 *
+	 * @param query
+	 * @param cursorRequest
+	 * @param idPropertyName
+	 * @return
+	 */
+	static KeySetCursorQuery createKeysetPaginationQuery(Query query, KeysetCursorRequest cursorRequest,
+			String idPropertyName) {
+
+		Sort targetSort = cursorRequest.getSort().and(Sort.by(Order.asc(idPropertyName)));
+
+		// make sure we can extract the keyset
+		Document fieldsObject = query.getFieldsObject();
+		if (!fieldsObject.isEmpty()) {
+			fieldsObject.put(idPropertyName, 1);
+			for (Order order : cursorRequest.getSort()) {
+				fieldsObject.put(order.getProperty(), 1);
+			}
+		}
+
+		Document sortObject = query.isSorted() ? query.getSortObject() : new Document();
+		targetSort.forEach(order -> sortObject.put(order.getProperty(), order.isAscending() ? 1 : -1));
+		sortObject.put(idPropertyName, 1);
+
+		Document queryObject = query.getQueryObject();
+
+		List<Document> or = (List<Document>) queryObject.getOrDefault("$or", new ArrayList<>());
+
+		Map<String, Object> keysetValues = cursorRequest.getKeys();
+		Document keysetSort = new Document();
+		List<String> sortKeys = new ArrayList<>(sortObject.keySet());
+
+		if (!keysetValues.isEmpty() && !keysetValues.keySet().containsAll(sortKeys)) {
+			throw new IllegalStateException("KeysetCursorRequest does not contain all keyset values");
+		}
+
+		// first query doesn't come with a keyset
+		if (!keysetValues.isEmpty()) {
+
+			// build matrix query for keyset paging that contains sort^2 queries
+			// reflecting a query that follows sort order semantics starting from the last returned keyset
+			for (int i = 0; i < sortKeys.size(); i++) {
+
+				Document sortConstraint = new Document();
+
+				for (int j = 0; j < sortKeys.size(); j++) {
+
+					String sortSegment = sortKeys.get(j);
+					int sortOrder = sortObject.getInteger(sortSegment);
+					Object o = keysetValues.get(sortSegment);
+
+					if (j >= i) { // tail segment
+						sortConstraint.put(sortSegment, new Document(sortOrder == 1 ? "$gt" : "$lt", o));
+						break;
+					}
+
+					sortConstraint.put(sortSegment, o);
+				}
+
+				if (!sortConstraint.isEmpty()) {
+					or.add(sortConstraint);
+				}
+			}
+		}
+
+		if (!keysetSort.isEmpty()) {
+			or.add(keysetSort);
+		}
+		if (!or.isEmpty()) {
+			queryObject.put("$or", or);
+		}
+
+		return new KeySetCursorQuery(queryObject, fieldsObject, sortObject);
+	}
+
+	static <T> CursorWindow<T> createWindow(KeysetCursorRequest cursorRequest, List<T> result,
+			EntityOperations operations) {
+
+		if (CursorUtils.hasMoreElements(cursorRequest, result)) {
+
+			T last = result.get(cursorRequest.getSize() - 1);
+			Entity<T> entity = operations.forEntity(last);
+
+			Map<String, Object> keys = entity.extractKeys(cursorRequest.getSort());
+			cursorRequest = cursorRequest.withNext(keys);
+		}
+
+		return createWindow(cursorRequest, result);
+	}
+
+	static <T> CursorWindow<T> createWindow(CursorRequest cursorRequest, List<T> result) {
 		return CursorWindow.from(cursorRequest.withLast(isLast(cursorRequest, result)), getSubList(cursorRequest, result));
 	}
+
+	record KeySetCursorQuery(Document query, Document fields, Document sort) {
+
+	}
+
 }

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

@@ -470,38 +470,6 @@ MongoCollection<Document> createView(String name, String source, AggregationPipe
 	 */
 	<T> List<T> findAll(Class<T> entityClass, String collectionName);
 
-	/**
-	 * Query for a cursor window of objects of type T from the specified collection. <br />
-	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
-	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used. <br />
-	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
-	 * to map objects since the test for class type is done in the client and not on the server.
-	 *
-	 * @param cursorRequest the cursor request.
-	 * @param entityType the parametrized type of the returned list.
-	 * @param collectionName name of the collection to retrieve the objects from.
-	 * @return the converted cursor window.
-	 * @see org.springframework.data.domain.OffsetCursorRequest
-	 * @see org.springframework.data.domain.KeysetCursorRequest
-	 */
-	<T> CursorWindow<T> findWindow(CursorRequest cursorRequest, Query query, Class<T> entityTypee);
-
-	/**
-	 * Query for a cursor window of objects of type T from the specified collection. <br />
-	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
-	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used. <br />
-	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
-	 * to map objects since the test for class type is done in the client and not on the server.
-	 *
-	 * @param cursorRequest the cursor request.
-	 * @param entityType the parametrized type of the returned list.
-	 * @param collectionName name of the collection to retrieve the objects from.
-	 * @return the converted cursor window.
-	 * @see org.springframework.data.domain.OffsetCursorRequest
-	 * @see org.springframework.data.domain.KeysetCursorRequest
-	 */
-	<T> CursorWindow<T> findWindow(CursorRequest cursorRequest, Query query, Class<T> entityType, String collectionName);
-
 	/**
 	 * Execute an aggregation operation. The raw results will be mapped to the given entity class. The name of the
 	 * inputCollection is derived from the inputType of the aggregation.
@@ -838,6 +806,43 @@ <T> MapReduceResults<T> mapReduce(Query query, String inputCollectionName, Strin
 	 */
 	<T> List<T> find(Query query, Class<T> entityClass, String collectionName);
 
+	/**
+	 * Query for a cursor window of objects of type T from the specified collection. <br />
+	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
+	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used. <br />
+	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
+	 * to map objects since the test for class type is done in the client and not on the server.
+	 *
+	 * @param cursorRequest the cursor request.
+	 * @param query the query class that specifies the criteria used to find a record and also an optional fields
+	 *          specification. Must not be {@literal null}.
+	 * @param entityType the parametrized type of the returned list.
+	 * @return the converted cursor window.
+	 * @since 4.1
+	 * @see org.springframework.data.domain.OffsetCursorRequest
+	 * @see org.springframework.data.domain.KeysetCursorRequest
+	 */
+	<T> CursorWindow<T> findWindow(CursorRequest cursorRequest, Query query, Class<T> entityType);
+
+	/**
+	 * Query for a cursor window of objects of type T from the specified collection. <br />
+	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
+	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used. <br />
+	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
+	 * to map objects since the test for class type is done in the client and not on the server.
+	 *
+	 * @param cursorRequest the cursor request.
+	 * @param query the query class that specifies the criteria used to find a record and also an optional fields
+	 *          specification. Must not be {@literal null}.
+	 * @param entityType the parametrized type of the returned list.
+	 * @param collectionName name of the collection to retrieve the objects from.
+	 * @return the converted cursor window.
+	 * @since 4.1
+	 * @see org.springframework.data.domain.OffsetCursorRequest
+	 * @see org.springframework.data.domain.KeysetCursorRequest
+	 */
+	<T> CursorWindow<T> findWindow(CursorRequest cursorRequest, Query query, Class<T> entityType, String collectionName);
+
 	/**
 	 * Returns a document with the given id mapped onto the given class. The collection the query is ran against will be
 	 * derived from the given target class as well.