Map collection and fields for $graphLookup aggregation against type.

This commit enables using a type parameter to define the from collection of a graphLookup aggregation stage. In doing so we can derive the target collection name from the type and use the given information to also map the from field against the domain object to so that the user is able to operate on property names instead of the target db field name.

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

@@ -46,7 +46,7 @@ public class GraphLookupOperation implements InheritsFieldsAggregationOperation
 	private static final Set<Class<?>> ALLOWED_START_TYPES = new HashSet<Class<?>>(
 			Arrays.<Class<?>> asList(AggregationExpression.class, String.class, Field.class, Document.class));
 
-	private final String from;
+	private final Object from;
 	private final List<Object> startWith;
 	private final Field connectFrom;
 	private final Field connectTo;
@@ -55,7 +55,7 @@ public class GraphLookupOperation implements InheritsFieldsAggregationOperation
 	private final @Nullable Field depthField;
 	private final @Nullable CriteriaDefinition restrictSearchWithMatch;
 
-	private GraphLookupOperation(String from, List<Object> startWith, Field connectFrom, Field connectTo, Field as,
+	private GraphLookupOperation(Object from, List<Object> startWith, Field connectFrom, Field connectTo, Field as,
 			@Nullable Long maxDepth, @Nullable Field depthField, @Nullable CriteriaDefinition restrictSearchWithMatch) {
 
 		this.from = from;
@@ -82,7 +82,7 @@ public Document toDocument(AggregationOperationContext context) {
 
 		Document graphLookup = new Document();
 
-		graphLookup.put("from", from);
+		graphLookup.put("from", getCollectionName(context));
 
 		List<Object> mappedStartWith = new ArrayList<>(startWith.size());
 
@@ -99,7 +99,7 @@ public Document toDocument(AggregationOperationContext context) {
 
 		graphLookup.put("startWith", mappedStartWith.size() == 1 ? mappedStartWith.iterator().next() : mappedStartWith);
 
-		graphLookup.put("connectFromField", connectFrom.getTarget());
+		graphLookup.put("connectFromField", getForeignFieldName(context));
 		graphLookup.put("connectToField", connectTo.getTarget());
 		graphLookup.put("as", as.getName());
 
@@ -118,6 +118,16 @@ public Document toDocument(AggregationOperationContext context) {
 		return new Document(getOperator(), graphLookup);
 	}
 
+	String getCollectionName(AggregationOperationContext context) {
+		return from instanceof Class<?> type ? context.getCollection(type) : from.toString();
+	}
+
+	String getForeignFieldName(AggregationOperationContext context) {
+
+		return from instanceof Class<?> type ? context.getMappedFieldName(type, connectFrom.getTarget())
+				: connectFrom.getTarget();
+	}
+
 	@Override
 	public String getOperator() {
 		return "$graphLookup";
@@ -128,7 +138,7 @@ public ExposedFields getFields() {
 
 		List<ExposedField> fields = new ArrayList<>(2);
 		fields.add(new ExposedField(as, true));
-		if(depthField != null) {
+		if (depthField != null) {
 			fields.add(new ExposedField(depthField, true));
 		}
 		return ExposedFields.from(fields.toArray(new ExposedField[0]));
@@ -146,6 +156,17 @@ public interface FromBuilder {
 		 * @return never {@literal null}.
 		 */
 		StartWithBuilder from(String collectionName);
+
+		/**
+		 * Use the given type to determine name of the foreign collection and map
+		 * {@link ConnectFromBuilder#connectFrom(String)} against it to consider eventually present
+		 * {@link org.springframework.data.mongodb.core.mapping.Field} annotations.
+		 *
+		 * @param type must not be {@literal null}.
+		 * @return never {@literal null}.
+		 * @since 4.2
+		 */
+		StartWithBuilder from(Class<?> type);
 	}
 
 	/**
@@ -218,7 +239,7 @@ public interface ConnectToBuilder {
 	static final class GraphLookupOperationFromBuilder
 			implements FromBuilder, StartWithBuilder, ConnectFromBuilder, ConnectToBuilder {
 
-		private @Nullable String from;
+		private @Nullable Object from;
 		private @Nullable List<? extends Object> startWith;
 		private @Nullable String connectFrom;
 
@@ -231,6 +252,14 @@ public StartWithBuilder from(String collectionName) {
 			return this;
 		}
 
+		@Override
+		public StartWithBuilder from(Class<?> type) {
+
+			Assert.notNull(type, "Type must not be null");
+			this.from = type;
+			return this;
+		}
+
 		@Override
 		public ConnectFromBuilder startWith(String... fieldReferences) {
 
@@ -321,15 +350,15 @@ public GraphLookupOperationBuilder connectTo(String fieldName) {
 	 */
 	public static final class GraphLookupOperationBuilder {
 
-		private final String from;
+		private final Object from;
 		private final List<Object> startWith;
 		private final Field connectFrom;
 		private final Field connectTo;
 		private @Nullable Long maxDepth;
 		private @Nullable Field depthField;
 		private @Nullable CriteriaDefinition restrictSearchWithMatch;
 
-		protected GraphLookupOperationBuilder(String from, List<? extends Object> startWith, String connectFrom,
+		protected GraphLookupOperationBuilder(Object from, List<? extends Object> startWith, String connectFrom,
 				String connectTo) {
 
 			this.from = from;

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/GraphLookupOperationUnitTests.java

@@ -22,6 +22,7 @@
 import org.bson.Document;
 import org.junit.jupiter.api.Test;
 import org.springframework.data.mongodb.core.Person;
+import org.springframework.data.mongodb.core.mapping.Field;
 import org.springframework.data.mongodb.core.query.Criteria;
 
 /**
@@ -34,7 +35,7 @@ public class GraphLookupOperationUnitTests {
 
 	@Test // DATAMONGO-1551
 	public void rejectsNullFromCollection() {
-		assertThatIllegalArgumentException().isThrownBy(() -> GraphLookupOperation.builder().from(null));
+		assertThatIllegalArgumentException().isThrownBy(() -> GraphLookupOperation.builder().from((String) null));
 	}
 
 	@Test // DATAMONGO-1551
@@ -158,4 +159,59 @@ public void depthFieldShouldUseTargetFieldInsteadOfAlias() {
 
 		assertThat(document).containsEntry("$graphLookup.depthField", "foo.bar");
 	}
+
+	@Test // GH-4379
+	void unmappedLookupWithFromExtractedFromType() {
+
+		GraphLookupOperation graphLookupOperation = GraphLookupOperation.builder() //
+				.from(Employee.class) //
+				.startWith(LiteralOperators.Literal.asLiteral("hello")) //
+				.connectFrom("manager") //
+				.connectTo("name") //
+				.as("reportingHierarchy");
+
+		assertThat(graphLookupOperation.toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo("""
+				{ $graphLookup:
+					{
+						from: "employee",
+						startWith : { $literal : "hello" },
+						connectFromField: "manager",
+						connectToField: "name",
+						as: "reportingHierarchy"
+					}
+				}}
+				""");
+	}
+
+	@Test // GH-4379
+	void mappedLookupWithFromExtractedFromType() {
+
+		GraphLookupOperation graphLookupOperation = GraphLookupOperation.builder() //
+				.from(Employee.class) //
+				.startWith(LiteralOperators.Literal.asLiteral("hello")) //
+				.connectFrom("manager") //
+				.connectTo("name") //
+				.as("reportingHierarchy");
+
+		assertThat(graphLookupOperation.toDocument(AggregationTestUtils.strict(Employee.class).ctx())).isEqualTo("""
+				{ $graphLookup:
+					{
+						from: "employees",
+						startWith : { $literal : "hello" },
+						connectFromField: "reportsTo",
+						connectToField: "name",
+						as: "reportingHierarchy"
+					}
+				}}
+				""");
+	}
+
+	@org.springframework.data.mongodb.core.mapping.Document("employees")
+	static class Employee {
+
+		String id;
+
+		@Field("reportsTo")
+		String manager;
+	}
 }