feat: spec for new BaseFilter

backend-core-data-impl/src/main/java/com/flowingcode/backendcore/dao/jpa/AttributePathResolver.java

@@ -0,0 +1,116 @@
+/*-
+ * #%L
+ * Commons Backend - Data Access Layer Implementations
+ * %%
+ * Copyright (C) 2020 - 2026 Flowing Code
+ * %%
+ * 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
+ *
+ *      http://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.
+ * #L%
+ */
+package com.flowingcode.backendcore.dao.jpa;
+
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.Optional;
+
+import jakarta.persistence.criteria.Expression;
+import jakarta.persistence.criteria.From;
+import jakarta.persistence.criteria.Join;
+import jakarta.persistence.criteria.JoinType;
+
+/**
+ * Resolves a dotted attribute path on a JPA {@code From} root into a leaf
+ * {@code Expression}, auto-joining associations along the way and reusing
+ * existing joins when one is already present on the same attribute and join
+ * type.
+ *
+ * <p>Instances are not thread-safe: a new resolver should be created per
+ * {@code CriteriaQuery}.
+ */
+public class AttributePathResolver {
+
+	private final From<?, ?> root;
+
+	private JoinType currentJoinType = JoinType.INNER;
+
+	public AttributePathResolver(From<?, ?> root) {
+		this.root = Objects.requireNonNull(root, "root");
+	}
+
+	/** Returns the join type currently used when creating new joins. */
+	public JoinType getCurrentJoinType() {
+		return currentJoinType;
+	}
+
+	/** Sets the join type used for newly created joins by subsequent resolutions. */
+	public void setCurrentJoinType(JoinType joinType) {
+		this.currentJoinType = Objects.requireNonNull(joinType, "joinType");
+	}
+
+	/**
+	 * Resolves {@code attributePath} into an {@code Expression} of the leaf
+	 * attribute on the root, auto-joining as needed.
+	 */
+	public Expression<?> resolve(String attributePath) {
+		return resolve(attributePath, Object.class);
+	}
+
+	/**
+	 * Resolves {@code attributePath} and verifies the leaf attribute's Java type
+	 * is assignable to {@code expectedType}.
+	 *
+	 * @throws ClassCastException if the leaf attribute type isn't compatible
+	 */
+	@SuppressWarnings("unchecked")
+	public <V> Expression<V> resolve(String attributePath, Class<V> expectedType) {
+		Objects.requireNonNull(attributePath, "attributePath");
+		String[] path = attributePath.split("\\.");
+		String attributeName = path[path.length - 1];
+		String[] joinPath = Arrays.copyOf(path, path.length - 1);
+		Expression<?> expression = traverse(root, joinPath).get(attributeName);
+		boxed(expression.getJavaType()).asSubclass(expectedType);
+		return (Expression<V>) expression;
+	}
+
+	private From<?, ?> traverse(From<?, ?> source, String[] path) {
+		From<?, ?> from = source;
+		for (String name : path) {
+			from = join(from, name);
+		}
+		return from;
+	}
+
+	@SuppressWarnings("rawtypes")
+	private From<?, ?> join(From<?, ?> source, String attributeName) {
+		Optional<Join> existing = source.getJoins().stream()
+				.map(j -> (Join) j)
+				.filter(j -> j.getAttribute().getName().equals(attributeName))
+				.filter(j -> j.getJoinType() == currentJoinType)
+				.findFirst();
+		return existing.orElseGet(() -> source.join(attributeName, currentJoinType));
+	}
+
+	private static Class<?> boxed(Class<?> type) {
+		if (type.isPrimitive()) {
+			if (type == boolean.class) return Boolean.class;
+			if (type == int.class) return Integer.class;
+			if (type == long.class) return Long.class;
+			if (type == byte.class) return Byte.class;
+			if (type == short.class) return Short.class;
+			if (type == char.class) return Character.class;
+			if (type == float.class) return Float.class;
+			if (type == double.class) return Double.class;
+		}
+		return type;
+	}
+}