add rel interface

core/src/main/java/com/datastrato/gravitino/Configs.java

@@ -11,11 +11,15 @@
 public interface Configs {
 
   String DEFAULT_ENTITY_STORE = "kv";
+  String RELATION_ENTITY_STORE = "rel";
   String ENTITY_STORE_KEY = "gravitino.entity.store";
 
   String DEFAULT_ENTITY_KV_STORE = "RocksDBKvBackend";
   String ENTITY_KV_STORE_KEY = "gravitino.entity.store.kv";
 
+  String DEFAULT_ENTITY_RELATION_STORE = "MysqlBackend";
+  String ENTITY_RELATION_STORE_KEY = "gravitino.entity.store.rel";
+
   String ENTITY_KV_ROCKSDB_BACKEND_PATH_KEY = "gravitino.entity.store.kv.rocksdbPath";
 
   Long DEFAULT_KV_DELETE_AFTER_TIME = 604800000L; // 7 days
@@ -45,6 +49,13 @@ public interface Configs {
           .stringConf()
           .createWithDefault(DEFAULT_ENTITY_KV_STORE);
 
+  ConfigEntry<String> ENTITY_RELATION_STORE =
+      new ConfigBuilder(ENTITY_RELATION_STORE_KEY)
+          .doc("Detailed implementation of relation storage")
+          .version("0.1.0")
+          .stringConf()
+          .createWithDefault(DEFAULT_ENTITY_RELATION_STORE);
+
   ConfigEntry<String> ENTRY_KV_ROCKSDB_BACKEND_PATH =
       new ConfigBuilder(ENTITY_KV_ROCKSDB_BACKEND_PATH_KEY)
           .doc("Directory path of `RocksDBKvBackend`")

core/src/main/java/com/datastrato/gravitino/EntityStoreFactory.java

@@ -5,6 +5,7 @@
 package com.datastrato.gravitino;
 
 import com.datastrato.gravitino.storage.kv.KvEntityStore;
+import com.datastrato.gravitino.storage.relation.RelationEntityStore;
 import com.google.common.collect.ImmutableMap;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -20,7 +21,11 @@ public class EntityStoreFactory {
   // Register EntityStore's short name to its full qualified class name in the map. So that user
   // doesn't need to specify the full qualified class name when creating an EntityStore.
   public static final ImmutableMap<String, String> ENTITY_STORES =
-      ImmutableMap.of("kv", KvEntityStore.class.getCanonicalName());
+      ImmutableMap.of(
+          "kv",
+          KvEntityStore.class.getCanonicalName(),
+          "rel",
+          RelationEntityStore.class.getCanonicalName());
 
   // Private constructor to prevent instantiation of this factory class.
   private EntityStoreFactory() {}

core/src/main/java/com/datastrato/gravitino/GravitinoEnv.java

@@ -12,6 +12,7 @@
 import com.datastrato.gravitino.metrics.source.JVMMetricsSource;
 import com.datastrato.gravitino.storage.IdGenerator;
 import com.datastrato.gravitino.storage.RandomIdGenerator;
+import com.datastrato.gravitino.storage.relation.RelationEntityStore;
 import com.google.common.base.Preconditions;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -74,7 +75,9 @@ public void initialize(Config config) {
     // Initialize EntityStore
     this.entityStore = EntityStoreFactory.createEntityStore(config);
     entityStore.initialize(config);
-    entityStore.setSerDe(entitySerDe);
+    if (!(entityStore instanceof RelationEntityStore)) {
+      entityStore.setSerDe(entitySerDe);
+    }
 
     // create and initialize a random id generator
     this.idGenerator = new RandomIdGenerator();

core/src/main/java/com/datastrato/gravitino/storage/relation/RelationBackend.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2024 Datastrato Pvt Ltd.
+ * This software is licensed under the Apache License version 2.
+ */
+package com.datastrato.gravitino.storage.relation;
+
+import com.datastrato.gravitino.Config;
+import com.datastrato.gravitino.Entity;
+import com.datastrato.gravitino.EntityAlreadyExistsException;
+import com.datastrato.gravitino.HasIdentifier;
+import com.datastrato.gravitino.NameIdentifier;
+import com.datastrato.gravitino.Namespace;
+import com.datastrato.gravitino.exceptions.AlreadyExistsException;
+import com.datastrato.gravitino.exceptions.NoSuchEntityException;
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.List;
+import java.util.function.Function;
+
+public interface RelationBackend extends Closeable {
+
+  void initialize(Config config) throws IOException;
+
+  <E extends Entity & HasIdentifier> List<E> list(Namespace namespace, Entity.EntityType entityType)
+      throws IOException;
+
+  boolean exists(NameIdentifier ident, Entity.EntityType entityType) throws IOException;
+
+  <E extends Entity & HasIdentifier> void put(E e, boolean overwritten)
+      throws IOException, EntityAlreadyExistsException;
+
+  <E extends Entity & HasIdentifier> E update(
+      NameIdentifier ident, Entity.EntityType entityType, Function<E, E> updater)
+      throws IOException, NoSuchEntityException, AlreadyExistsException;
+
+  <E extends Entity & HasIdentifier> E get(NameIdentifier ident, Entity.EntityType entityType)
+      throws NoSuchEntityException, IOException;
+
+  boolean delete(NameIdentifier ident, Entity.EntityType entityType, boolean cascade)
+      throws IOException;
+}

core/src/main/java/com/datastrato/gravitino/storage/relation/RelationEntityStore.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2024 Datastrato Pvt Ltd.
+ * This software is licensed under the Apache License version 2.
+ */
+package com.datastrato.gravitino.storage.relation;
+
+import static com.datastrato.gravitino.Configs.ENTITY_RELATION_STORE;
+
+import com.datastrato.gravitino.Config;
+import com.datastrato.gravitino.Entity;
+import com.datastrato.gravitino.EntityAlreadyExistsException;
+import com.datastrato.gravitino.EntitySerDe;
+import com.datastrato.gravitino.EntityStore;
+import com.datastrato.gravitino.HasIdentifier;
+import com.datastrato.gravitino.NameIdentifier;
+import com.datastrato.gravitino.Namespace;
+import com.datastrato.gravitino.exceptions.AlreadyExistsException;
+import com.datastrato.gravitino.exceptions.NoSuchEntityException;
+import com.datastrato.gravitino.storage.relation.mysql.MysqlBackend;
+import com.datastrato.gravitino.utils.Executable;
+import com.google.common.collect.ImmutableMap;
+import java.io.IOException;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Function;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class RelationEntityStore implements EntityStore {
+  private static final Logger LOGGER = LoggerFactory.getLogger(RelationEntityStore.class);
+  public static final ImmutableMap<String, String> RELATION_BACKENDS =
+      ImmutableMap.of("MysqlBackend", MysqlBackend.class.getCanonicalName());
+  private RelationBackend backend;
+
+  @Override
+  public void initialize(Config config) throws RuntimeException {
+    this.backend = createRelationEntityBackend(config);
+  }
+
+  private static RelationBackend createRelationEntityBackend(Config config) {
+    String backendName = config.get(ENTITY_RELATION_STORE);
+    String className = RELATION_BACKENDS.getOrDefault(backendName, backendName);
+    if (Objects.isNull(className)) {
+      throw new RuntimeException("Unsupported backend type..." + backendName);
+    }
+
+    try {
+      RelationBackend relationBackend =
+          (RelationBackend) Class.forName(className).getDeclaredConstructor().newInstance();
+      relationBackend.initialize(config);
+      return relationBackend;
+    } catch (Exception e) {
+      LOGGER.error("Failed to create and initialize RelationBackend by name '{}'.", backendName, e);
+      throw new RuntimeException(
+          "Failed to create and initialize RelationBackend by name: " + backendName, e);
+    }
+  }
+
+  @Override
+  public void setSerDe(EntitySerDe entitySerDe) {
+    throw new UnsupportedOperationException("Unsupported operation in relation entity store.");
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> List<E> list(
+      Namespace namespace, Class<E> type, Entity.EntityType entityType) throws IOException {
+    return backend.list(namespace, entityType);
+  }
+
+  @Override
+  public boolean exists(NameIdentifier ident, Entity.EntityType entityType) throws IOException {
+    return backend.exists(ident, entityType);
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> void put(E e, boolean overwritten)
+      throws IOException, EntityAlreadyExistsException {
+    backend.put(e, overwritten);
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> E update(
+      NameIdentifier ident, Class<E> type, Entity.EntityType entityType, Function<E, E> updater)
+      throws IOException, NoSuchEntityException, AlreadyExistsException {
+    return backend.update(ident, entityType, updater);
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> E get(
+      NameIdentifier ident, Entity.EntityType entityType, Class<E> e)
+      throws NoSuchEntityException, IOException {
+    return backend.get(ident, entityType);
+  }
+
+  @Override
+  public boolean delete(NameIdentifier ident, Entity.EntityType entityType, boolean cascade)
+      throws IOException {
+    return backend.delete(ident, entityType, cascade);
+  }
+
+  @Override
+  public <R, E extends Exception> R executeInTransaction(Executable<R, E> executable)
+      throws E, IOException {
+    throw new UnsupportedOperationException("Unsupported operation in relation entity store.");
+  }
+
+  @Override
+  public void close() throws IOException {
+    backend.close();
+  }
+}

core/src/main/java/com/datastrato/gravitino/storage/relation/mysql/MysqlBackend.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2024 Datastrato Pvt Ltd.
+ * This software is licensed under the Apache License version 2.
+ */
+package com.datastrato.gravitino.storage.relation.mysql;
+
+import com.datastrato.gravitino.Config;
+import com.datastrato.gravitino.Entity;
+import com.datastrato.gravitino.EntityAlreadyExistsException;
+import com.datastrato.gravitino.HasIdentifier;
+import com.datastrato.gravitino.NameIdentifier;
+import com.datastrato.gravitino.Namespace;
+import com.datastrato.gravitino.exceptions.AlreadyExistsException;
+import com.datastrato.gravitino.exceptions.NoSuchEntityException;
+import com.datastrato.gravitino.storage.relation.RelationBackend;
+import java.io.IOException;
+import java.util.List;
+import java.util.function.Function;
+
+public class MysqlBackend implements RelationBackend {
+  @Override
+  public void initialize(Config config) throws IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> List<E> list(
+      Namespace namespace, Entity.EntityType entityType) throws IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public boolean exists(NameIdentifier ident, Entity.EntityType entityType) throws IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> void put(E e, boolean overwritten)
+      throws IOException, EntityAlreadyExistsException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> E update(
+      NameIdentifier ident, Entity.EntityType entityType, Function<E, E> updater)
+      throws IOException, NoSuchEntityException, AlreadyExistsException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public <E extends Entity & HasIdentifier> E get(
+      NameIdentifier ident, Entity.EntityType entityType)
+      throws NoSuchEntityException, IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public boolean delete(NameIdentifier ident, Entity.EntityType entityType, boolean cascade)
+      throws IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+
+  @Override
+  public void close() throws IOException {
+    throw new UnsupportedOperationException("Unsupported operation now.");
+  }
+}