Add a test showing how to write paginated queries

Author: jeffgbutler

src/test/java/examples/paging/LimitAndOffsetAdapter.java

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+/**
+ *    Copyright 2016-2018 the original author or authors.
+ *
+ *    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.
+ */
+package examples.paging;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.function.Function;
+
+import org.mybatis.dynamic.sql.render.RenderingStrategy;
+import org.mybatis.dynamic.sql.select.SelectModel;
+import org.mybatis.dynamic.sql.select.render.SelectStatementProvider;
+
+/**
+ * This adapter modifies the generated SQL by adding a LIMIT and OFFSET clause at the end
+ * of the generated SQL.  This can be used to create a paginated query.
+ * 
+ * LIMIT and OFFSET has limited support in relational databases, so this cannot be considered
+ * a general solution for all paginated queries (and that is why this adapter lives only in the
+ * test source tree and is not packaged with the core library code).
+ * 
+ * I believe it works in MySQL, HSQLDB, and Postgres.
+ * 
+ * @author Jeff Butler
+ */
+public class LimitAndOffsetAdapter<R> {
+    private SelectModel selectModel;
+    private Function<SelectStatementProvider, R> mapperMethod;
+    private int limit;
+    private int offset;
+    
+    private LimitAndOffsetAdapter(SelectModel selectModel, Function<SelectStatementProvider, R> mapperMethod,
+            int limit, int offset) {
+        this.selectModel = Objects.requireNonNull(selectModel);
+        this.mapperMethod = Objects.requireNonNull(mapperMethod);
+        this.limit = limit;
+        this.offset = offset;
+    }
+    
+    public R execute() {
+        return mapperMethod.apply(selectStatement());
+    }
+    
+    private SelectStatementProvider selectStatement() {
+        return new LimitAndOffsetDecorator(
+                selectModel.render(RenderingStrategy.MYBATIS3));
+    }
+    
+    public static <R> LimitAndOffsetAdapter<R> of(SelectModel selectModel,
+            Function<SelectStatementProvider, R> mapperMethod, int limit, int offset) {
+        return new LimitAndOffsetAdapter<>(selectModel, mapperMethod, limit, offset);
+    }
+    
+    public class LimitAndOffsetDecorator implements SelectStatementProvider {
+        private Map<String, Object> parameters = new HashMap<>();
+        private String selectStatement;
+        
+        public LimitAndOffsetDecorator(SelectStatementProvider delegate) {
+            parameters.putAll(delegate.getParameters());
+            parameters.put("limit", limit);
+            parameters.put("offset", offset);
+            
+            selectStatement = delegate.getSelectStatement() +
+                    " LIMIT #{parameters.limit} OFFSET #{parameters.offset}";
+        }
+
+        @Override
+        public Map<String, Object> getParameters() {
+            return parameters;
+        }
+
+        @Override
+        public String getSelectStatement() {
+            return selectStatement;
+        }
+    }
+}

src/test/java/examples/paging/LimitAndOffsetMapper.java

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+/**
+ *    Copyright 2016-2018 the original author or authors.
+ *
+ *    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.
+ */
+package examples.paging;
+
+import static examples.animal.data.AnimalDataDynamicSqlSupport.*;
+
+import java.util.List;
+
+import org.apache.ibatis.annotations.Result;
+import org.apache.ibatis.annotations.Results;
+import org.apache.ibatis.annotations.SelectProvider;
+import org.mybatis.dynamic.sql.select.QueryExpressionDSL;
+import org.mybatis.dynamic.sql.select.SelectDSL;
+import org.mybatis.dynamic.sql.select.render.SelectStatementProvider;
+import org.mybatis.dynamic.sql.util.SqlProviderAdapter;
+
+import examples.animal.data.AnimalData;
+
+public interface LimitAndOffsetMapper {
+
+    @SelectProvider(type=SqlProviderAdapter.class, method="select")
+    @Results(id="AnimalDataResult", value={
+        @Result(column="id", property="id", id=true),
+        @Result(column="animal_name", property="animalName"),
+        @Result(column="brain_weight", property="brainWeight"),
+        @Result(column="body_weight", property="bodyWeight")
+    })
+    List<AnimalData> selectMany(SelectStatementProvider selectStatement);
+
+    default QueryExpressionDSL<LimitAndOffsetAdapter<List<AnimalData>>> selectByExampleWithLimitAndOffset(int limit, int offset) {
+        return SelectDSL.select(selectModel -> LimitAndOffsetAdapter.of(selectModel, this::selectMany, limit, offset),
+                id, animalName, brainWeight, bodyWeight)
+                .from(animalData);
+    }
+}

src/test/java/examples/paging/LimitAndOffsetTest.java

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+/**
+ *    Copyright 2016-2018 the original author or authors.
+ *
+ *    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.
+ */
+package examples.paging;
+
+import static examples.animal.data.AnimalDataDynamicSqlSupport.*;
+import static org.assertj.core.api.Assertions.*;
+
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.util.List;
+
+import org.apache.ibatis.datasource.unpooled.UnpooledDataSource;
+import org.apache.ibatis.jdbc.ScriptRunner;
+import org.apache.ibatis.mapping.Environment;
+import org.apache.ibatis.session.Configuration;
+import org.apache.ibatis.session.SqlSession;
+import org.apache.ibatis.session.SqlSessionFactory;
+import org.apache.ibatis.session.SqlSessionFactoryBuilder;
+import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.platform.runner.JUnitPlatform;
+import org.junit.runner.RunWith;
+
+import examples.animal.data.AnimalData;
+
+@RunWith(JUnitPlatform.class)
+public class LimitAndOffsetTest {
+    
+    private static final String JDBC_URL = "jdbc:hsqldb:mem:aname";
+    private static final String JDBC_DRIVER = "org.hsqldb.jdbcDriver"; 
+    
+    private SqlSessionFactory sqlSessionFactory;
+    
+    @BeforeEach
+    public void setup() throws Exception {
+        Class.forName(JDBC_DRIVER);
+        InputStream is = getClass().getResourceAsStream("/examples/animal/data/CreateAnimalData.sql");
+        try (Connection connection = DriverManager.getConnection(JDBC_URL, "sa", "")) {
+            ScriptRunner sr = new ScriptRunner(connection);
+            sr.setLogWriter(null);
+            sr.runScript(new InputStreamReader(is));
+        }
+        
+        UnpooledDataSource ds = new UnpooledDataSource(JDBC_DRIVER, JDBC_URL, "sa", "");
+        Environment environment = new Environment("test", new JdbcTransactionFactory(), ds);
+        Configuration config = new Configuration(environment);
+        config.addMapper(LimitAndOffsetMapper.class);
+        sqlSessionFactory = new SqlSessionFactoryBuilder().build(config);
+    }
+    
+    @Test
+    public void testLimitandOffset() {
+        try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
+            LimitAndOffsetMapper mapper = sqlSession.getMapper(LimitAndOffsetMapper.class);
+            
+            List<AnimalData> rows = mapper.selectByExampleWithLimitAndOffset(5, 3)
+                    .orderBy(id)
+                    .build()
+                    .execute();
+            
+            assertThat(rows.size()).isEqualTo(5);
+            assertThat(rows.get(0).getId()).isEqualTo(4);
+        }
+    }
+}