Introduce an interface for Property. [improvement]

This change brings symmetry to the three things that make up a graph

- Nodes
- Relationships
- Properties

This change spares us from a further ABI incompatible change after 2021.1.0.

neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/AbstractPropertyContainer.java

@@ -40,12 +40,12 @@ public final Property property(String name) {
 
 	@Override
 	public final Property property(String... names) {
-		return Property.create(this, names);
+		return InternalPropertyImpl.create(this, names);
 	}
 
 	@Override
 	public final Property property(Expression lookup) {
-		return Property.create(this, lookup);
+		return InternalPropertyImpl.create(this, lookup);
 	}
 
 	@Override

neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/Cypher.java

@@ -140,7 +140,7 @@ public static Property property(String containerName, String... names) {
 	 * @return A new property.
 	 */
 	public static Property property(Expression expression, String... names) {
-		return Property.create(expression, names);
+		return InternalPropertyImpl.create(expression, names);
 	}
 
 	/**
@@ -166,7 +166,7 @@ public static Property property(String containerName, Expression lookup) {
 	 * @since 2021.0.0
 	 */
 	public static Property property(Expression expression, Expression lookup) {
-		return Property.create(expression, lookup);
+		return InternalPropertyImpl.create(expression, lookup);
 	}
 
 	/**

neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/Expression.java

@@ -353,6 +353,6 @@ default SortItem ascending() {
 	 */
 	default Property property(String... names) {
 
-		return Property.create(this, names);
+		return InternalPropertyImpl.create(this, names);
 	}
 }

neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/InternalPropertyImpl.java

@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2019-2021 "Neo4j,"
+ * Neo4j Sweden AB [https://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * 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.neo4j.cypherdsl.core;
+
+import static org.apiguardian.api.API.Status.INTERNAL;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import org.apiguardian.api.API;
+import org.neo4j.cypherdsl.core.support.Visitor;
+import org.neo4j.cypherdsl.core.utils.Assertions;
+
+@API(status = INTERNAL, since = "2021.1.0")
+final class InternalPropertyImpl implements Property {
+
+	static Property create(Named parentContainer, String... names) {
+
+		SymbolicName requiredSymbolicName = extractRequiredSymbolicName(parentContainer);
+		return new InternalPropertyImpl(Optional.of(parentContainer), requiredSymbolicName, createListOfChainedNames(names), null);
+	}
+
+	static Property create(Expression containerReference, String... names) {
+
+		Assertions.notNull(containerReference, "The property container is required.");
+		return new InternalPropertyImpl(Optional.empty(), containerReference, createListOfChainedNames(names), null);
+	}
+
+	static Property create(Named parentContainer, Expression lookup) {
+
+		SymbolicName requiredSymbolicName = extractRequiredSymbolicName(parentContainer);
+		return new InternalPropertyImpl(Optional.of(parentContainer), requiredSymbolicName,
+			Collections.singletonList(PropertyLookup.forExpression(lookup)), null);
+	}
+
+	static Property create(Expression containerReference, Expression lookup) {
+
+		return new InternalPropertyImpl(Optional.empty(), containerReference,
+			Collections.singletonList(PropertyLookup.forExpression(lookup)), null);
+	}
+
+	/**
+	 * The reference to the container itself is optional.
+	 */
+	private final Named container;
+
+	/**
+	 * The expression pointing to the {@link #container} above is not.
+	 */
+	private final Expression containerReference;
+
+	/**
+	 * The name of this property.
+	 */
+	private final List<PropertyLookup> names;
+
+	/**
+	 * An optional, external (as in external to the graph) reference.
+	 */
+	private final String externalReference;
+
+	InternalPropertyImpl(Optional<Named> container, Expression containerReference, List<PropertyLookup> names,
+		String externalReference) {
+
+		this.container = container.orElse(null);
+		this.containerReference = containerReference;
+		this.names = names;
+		this.externalReference = externalReference;
+	}
+
+	@Override
+	public List<PropertyLookup> getNames() {
+		return names;
+	}
+
+	@Override
+	public Named getContainer() {
+		return container;
+	}
+
+	@Override
+	public String getName() {
+		return externalReference != null ?
+			this.externalReference :
+			this.names.stream().map(PropertyLookup::getPropertyKeyName)
+				.map(SymbolicName::getValue)
+				.collect(Collectors.joining("."));
+	}
+
+	@Override
+	public Property referencedAs(String newReference) {
+
+		return new InternalPropertyImpl(Optional.ofNullable(this.container), containerReference, this.names,
+			newReference);
+	}
+
+	@Override
+	public Operation to(Expression expression) {
+		return Operations.set(this, expression);
+	}
+
+	@Override
+	public void accept(Visitor visitor) {
+		visitor.enter(this);
+		this.containerReference.accept(visitor);
+		this.names.forEach(name -> name.accept(visitor));
+		visitor.leave(this);
+	}
+
+	private static List<PropertyLookup> createListOfChainedNames(String... names) {
+
+		Assertions.notEmpty(names, "The properties name is required.");
+
+		if (names.length == 1) {
+			return Collections.singletonList(PropertyLookup.forName(names[0]));
+		} else {
+			return Arrays.stream(names).map(PropertyLookup::forName)
+				.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
+		}
+	}
+
+	private static SymbolicName extractRequiredSymbolicName(Named parentContainer) {
+		try {
+			return parentContainer.getRequiredSymbolicName();
+		} catch (IllegalStateException e) {
+			throw new IllegalArgumentException(
+				"A property derived from a node or a relationship needs a parent with a symbolic name.");
+		}
+	}
+}

neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/Property.java

@@ -19,131 +19,47 @@
 package org.neo4j.cypherdsl.core;
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
-import static org.apiguardian.api.API.Status.INTERNAL;
 
-import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
-import java.util.Optional;
-import java.util.stream.Collectors;
 
 import org.apiguardian.api.API;
-import org.neo4j.cypherdsl.core.support.Visitor;
-import org.neo4j.cypherdsl.core.utils.Assertions;
 
 /**
  * A property. A property might belong to a container such as a {@link Node} or {@link Relationship}, but it's not uncommon
  * to extract single properties from maps or from various datatypes such as a duration returned from stored procedures.
  * The container can be retrieved via {@link #getContainer()} in case the property belongs to a node or relationship.
  * <p>
- * A property has always a reference to the name of the object it was extracted from (see {@link #containerReference}.
+ * A property has always a reference to the name of the object it was extracted from.
  *
  * @author Michael J. Simons
  * @since 1.0
  */
 @API(status = EXPERIMENTAL, since = "1.0")
-public final class Property implements Expression {
-
-	static Property create(Named parentContainer, String... names) {
-
-		SymbolicName requiredSymbolicName = extractRequiredSymbolicName(parentContainer);
-		return new Property(Optional.of(parentContainer), requiredSymbolicName, createListOfChainedNames(names), null);
-	}
-
-	static Property create(Expression containerReference, String... names) {
-
-		Assertions.notNull(containerReference, "The property container is required.");
-		return new Property(Optional.empty(), containerReference, createListOfChainedNames(names), null);
-	}
-
-	static Property create(Named parentContainer, Expression lookup) {
-
-		SymbolicName requiredSymbolicName = extractRequiredSymbolicName(parentContainer);
-		return new Property(Optional.of(parentContainer), requiredSymbolicName,
-			Collections.singletonList(PropertyLookup.forExpression(lookup)), null);
-	}
-
-	static Property create(Expression containerReference, Expression lookup) {
-
-		return new Property(Optional.empty(), containerReference,
-			Collections.singletonList(PropertyLookup.forExpression(lookup)), null);
-	}
-
-	private static List<PropertyLookup> createListOfChainedNames(String... names) {
-
-		Assertions.notEmpty(names, "The properties name is required.");
-
-		if (names.length == 1) {
-			return Collections.singletonList(PropertyLookup.forName(names[0]));
-		} else {
-			return Arrays.stream(names).map(PropertyLookup::forName)
-				.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
-		}
-	}
-
-	/**
-	 * The reference to the container itself is optional.
-	 */
-	private final Named container;
+public interface Property extends Expression {
 
 	/**
-	 * The expression pointing to the {@link #container} above is not.
-	 */
-	private final Expression containerReference;
-
-	/**
-	 * The name of this property.
-	 */
-	private final List<PropertyLookup> names;
-
-	/**
-	 * An optional, external (as in external to the graph) reference.
+	 * Returns the concatenated names of the property or the external reference (See {@link #referencedAs(String)}) if set.
+	 *
+	 * @return A name to reference the property under in an external application
 	 */
-	private final String externalReference;
-
-	Property(Optional<Named> container, Expression containerReference, List<PropertyLookup> names, String externalReference) {
-
-		this.container = container.orElse(null);
-		this.containerReference = containerReference;
-		this.names = names;
-		this.externalReference = externalReference;
-	}
+	@API(status = EXPERIMENTAL, since = "2021.1.0")
+	String getName();
 
 	/**
 	 * @return The actual property being looked up. The order matters, so this will return a list, not a collection.
 	 */
-	@API(status = INTERNAL)
-	List<PropertyLookup> getNames() {
-		return names;
-	}
+	List<PropertyLookup> getNames();
 
-	@API(status = INTERNAL)
-	Named getContainer() {
-		return container;
-	}
-
-	/**
-	 * Returns the concatenated names of the property or the {@link #externalReference} (See {@link #referencedAs(String)}) if set.
-	 *
-	 * @return A name to reference the property under in an external application
-	 */
-	@API(status = EXPERIMENTAL, since = "2021.1.0")
-	public String getName() {
-		return externalReference != null ? this.externalReference : this.names.stream().map(PropertyLookup::getPropertyKeyName)
-			.map(SymbolicName::getValue)
-			.collect(Collectors.joining("."));
-	}
+	Named getContainer();
 
 	/**
 	 * Creates a new property with an external reference.
+	 *
 	 * @param newReference An arbitrary, external reference
 	 * @return A new property
 	 */
 	@API(status = EXPERIMENTAL, since = "2021.1.0")
-	public Property referencedAs(String newReference) {
-
-		return new Property(Optional.ofNullable(this.container), containerReference, this.names, newReference);
-	}
+	Property referencedAs(String newReference);
 
 	/**
 	 * Creates an {@link Operation} setting this property to a new value. The property does not track the operations
@@ -152,24 +68,5 @@ public Property referencedAs(String newReference) {
 	 * @param expression expression describing the new value
 	 * @return A new operation.
 	 */
-	public Operation to(Expression expression) {
-		return Operations.set(this, expression);
-	}
-
-	@Override
-	public void accept(Visitor visitor) {
-		visitor.enter(this);
-		this.containerReference.accept(visitor);
-		this.names.forEach(name -> name.accept(visitor));
-		visitor.leave(this);
-	}
-
-	private static SymbolicName extractRequiredSymbolicName(Named parentContainer) {
-		try {
-			return parentContainer.getRequiredSymbolicName();
-		} catch (IllegalStateException e) {
-			throw new IllegalArgumentException(
-				"A property derived from a node or a relationship needs a parent with a symbolic name.");
-		}
-	}
+	Operation to(Expression expression);
 }

neo4j-cypher-dsl/src/test/java/org/neo4j/cypherdsl/core/FunctionsIT.java

@@ -96,7 +96,7 @@ void manual() {
 				.returning(
 					Functions.reduce(n)
 						.in(Functions.nodes(p))
-						.map(totalAge.add(Property.create(n, "age")))
+						.map(totalAge.add(Cypher.property(n, "age")))
 						.accumulateOn(totalAge)
 						.withInitialValueOf(Cypher.literalOf(0)).as("reduction")
 				).build();

neo4j-cypher-dsl/src/test/java/org/neo4j/cypherdsl/core/PropertyTest.java → neo4j-cypher-dsl/src/test/java/org/neo4j/cypherdsl/core/InternalPropertyImplTest.java

@@ -25,24 +25,24 @@
 /**
  * @author Michael J. Simons
  */
-class PropertyTest {
+class InternalPropertyImplTest {
 
 	@Test
 	void simplePropertyGetNameShouldWork() {
 
-		assertThat(Property.create(SymbolicName.unresolved(), "simple").getName()).isEqualTo("simple");
+		assertThat(InternalPropertyImpl.create(SymbolicName.unresolved(), "simple").getName()).isEqualTo("simple");
 	}
 
 	@Test
 	void multiplePropertyGetNameShouldWork() {
 
-		assertThat(Property.create(SymbolicName.unresolved(), "foo", "bar").getName()).isEqualTo("foo.bar");
+		assertThat(InternalPropertyImpl.create(SymbolicName.unresolved(), "foo", "bar").getName()).isEqualTo("foo.bar");
 	}
 
 	@Test
 	void externalReferenceHasPriority() {
 
-		assertThat(Property.create(SymbolicName.unresolved(), "foo", "bar").referencedAs("something")
+		assertThat(InternalPropertyImpl.create(SymbolicName.unresolved(), "foo", "bar").referencedAs("something")
 			.getName()).isEqualTo("something");
 	}
 }