[CALCITE-7022] Decouple ModelHandler from CalciteConnection

ModelHandler is mainly a parser that can transform YAML/JSON files into SchemaPlus objects.

Currently, the class requires a CalciteConnection in order to be instantiated and the latter is a pretty heavyweight object. The usage of the CalciteConnection makes it rather cumbersome to instantiate and use the parsing capabilities of the ModelHander independently.

In reality though, the handler does not need much from the CalciteConnection and we could easily refactor the handler to not depend on the connection at all.

The motivation for this change is to facilitate the creation of schema objects from YAML/JSON files.

Author: zabetak

core/src/main/java/org/apache/calcite/jdbc/Driver.java

@@ -144,7 +144,11 @@ protected Function0<CalcitePrepare> createPrepareFactory() {
         final String model = model(connection);
         if (model != null) {
           try {
-            new ModelHandler(connection, model);
+            ModelHandler h = new ModelHandler(connection.getRootSchema(), model);
+            String defaultName = h.defaultSchemaName();
+            if (defaultName != null) {
+              connection.setSchema(defaultName);
+            }
           } catch (IOException e) {
             throw new SQLException(e);
           }

core/src/main/java/org/apache/calcite/model/ModelHandler.java

@@ -77,20 +77,19 @@ public class ModelHandler {
       .configure(JsonParser.Feature.ALLOW_COMMENTS, true);
   private static final ObjectMapper YAML_MAPPER = new YAMLMapper();
 
-  private final CalciteConnection connection;
+  private final SchemaPlus rootSchema;
+  private final @Nullable String defaultSchemaName;
   private final Deque<Pair<? extends @Nullable String, SchemaPlus>> schemaStack =
       new ArrayDeque<>();
   private final String modelUri;
   Lattice.@Nullable Builder latticeBuilder;
   Lattice.@Nullable TileBuilder tileBuilder;
 
   @SuppressWarnings("method.invocation.invalid")
-  public ModelHandler(CalciteConnection connection, String uri)
-      throws IOException {
+  public ModelHandler(SchemaPlus rootSchema, String uri) throws IOException {
     super();
-    this.connection = connection;
     this.modelUri = uri;
-
+    this.rootSchema = rootSchema;
     JsonRoot root;
     ObjectMapper mapper;
     if (uri.startsWith("inline:")) {
@@ -105,6 +104,19 @@ public ModelHandler(CalciteConnection connection, String uri)
       root = mapper.readValue(new File(uri), JsonRoot.class);
     }
     visit(root);
+    this.defaultSchemaName = root.defaultSchema;
+  }
+
+  @Deprecated // to be removed before 2.0
+  public ModelHandler(CalciteConnection connection, String uri) throws IOException {
+    this(connection.getRootSchema(), uri);
+    if (defaultSchemaName != null) {
+      try {
+        connection.setSchema(defaultSchemaName);
+      } catch (SQLException e) {
+        throw new RuntimeException(e);
+      }
+    }
   }
 
   // CHECKSTYLE: IGNORE 1
@@ -196,7 +208,7 @@ public static void addFunctions(SchemaPlus schema,
 
   public void visit(JsonRoot jsonRoot) {
     final Pair<@Nullable String, SchemaPlus> pair =
-        Pair.of(null, connection.getRootSchema());
+        Pair.of(null, rootSchema);
     schemaStack.push(pair);
     for (JsonType rootType : jsonRoot.types) {
       rootType.accept(this);
@@ -206,13 +218,6 @@ public void visit(JsonRoot jsonRoot) {
     }
     final Pair<? extends @Nullable String, SchemaPlus> p = schemaStack.pop();
     assert p == pair;
-    if (jsonRoot.defaultSchema != null) {
-      try {
-        connection.setSchema(jsonRoot.defaultSchema);
-      } catch (SQLException e) {
-        throw new RuntimeException(e);
-      }
-    }
   }
 
   public void visit(JsonMapSchema jsonSchema) {
@@ -473,6 +478,10 @@ private SchemaPlus currentMutableSchema(String elementType) {
     return schema;
   }
 
+  public @Nullable String defaultSchemaName() {
+    return this.defaultSchemaName;
+  }
+
   public void visit(final JsonType jsonType) {
     try {
       final SchemaPlus schema = currentMutableSchema("type");

core/src/test/java/org/apache/calcite/model/ModelHandlerTest.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you 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.
+ */
+package org.apache.calcite.model;
+
+import org.apache.calcite.jdbc.CalciteSchema;
+import org.apache.calcite.schema.SchemaPlus;
+import org.apache.calcite.schema.lookup.LikePattern;
+import org.apache.calcite.util.Sources;
+
+import com.google.common.collect.ImmutableSet;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.util.Set;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * Unit test for {@link ModelHandler}.
+ */
+public class ModelHandlerTest {
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7022">[CALCITE-7022]
+   * Decouple ModelHandler from CalciteConnection</a>.
+   * The test ensures/demonstrates that a Schema can be easily parsed/created from a model
+   * file (JSON/YAML) without necessitating the creation of complex/heavy objects
+   * (e.g., CalciteConnection). */
+  @Test void testPopulateRootSchemaFromURL() throws IOException {
+    SchemaPlus root = CalciteSchema.createRootSchema(false, false).plus();
+    String mURI =
+        Sources.of(requireNonNull(ModelHandlerTest.class.getResource("/hsqldb-scott.json")))
+            .path();
+    ModelHandler h = new ModelHandler(root, mURI);
+    SchemaPlus scott = root.subSchemas().get("SCOTT");
+    Set<String> tables = scott.tables().getNames(new LikePattern("%"));
+    assertThat(tables, is(ImmutableSet.of("EMP", "DEPT", "BONUS", "SALGRADE")));
+    assertThat(h.defaultSchemaName(), is("SCOTT"));
+  }
+
+}

core/src/test/resources/hsqldb-scott.json

@@ -0,0 +1,28 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you 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.
+ */
+{
+  "version": "1.0",
+  "defaultSchema": "SCOTT",
+  "schemas": [ {
+    "type": "jdbc",
+    "name": "SCOTT",
+    "jdbcUser": "SA",
+    "jdbcPassword": "",
+    "jdbcUrl": "jdbc:hsqldb:res:scott",
+    "jdbcSchema": "SCOTT"
+  } ]
+}