#1405 - ENH: Add SqlQuery.findSingleAttribute() ... for returning single scalar values via SqlQuery

src/main/java/io/ebean/SqlQuery.java

@@ -83,6 +83,23 @@ public interface SqlQuery extends Serializable {
   @Nonnull
   Optional<SqlRow> findOneOrEmpty();
 
+  /**
+   * Execute the query returning a single scalar attribute.
+   * <pre>@{code
+   *
+   *   String sql = "select max(unit_price) from o_order_detail where order_qty > ?";
+   *
+   *   BigDecimal maxPrice = Ebean.createSqlQuery(sql)
+   *     .setParameter(1, 2)
+   *     .findSingleAttribute(BigDecimal.class);
+   *
+   *
+   * }</pre>
+   *
+   * @param attributeType The type of the returned value
+   */
+  <T> T findSingleAttribute(Class<T> attributeType);
+
   /**
    * The same as bind for named parameters.
    */

src/main/java/io/ebeaninternal/api/SpiEbeanServer.java

@@ -234,6 +234,11 @@ public interface SpiEbeanServer extends EbeanServer, BeanLoader, BeanCollectionL
    */
   void scopedTransactionExit(Object returnOrThrowable, int opCode);
 
+  /**
+   * SqlQuery find single attribute.
+   */
+  <T> T findSingleAttribute(SpiSqlQuery query, Class<T> cls);
+
   /**
    * DTO findList query.
    */

src/main/java/io/ebeaninternal/server/core/DefaultServer.java

@@ -67,6 +67,7 @@ import io.ebeaninternal.api.SpiJsonContext;
 import io.ebeaninternal.api.SpiLogManager;
 import io.ebeaninternal.api.SpiQuery;
 import io.ebeaninternal.api.SpiQuery.Type;
+import io.ebeaninternal.api.SpiSqlQuery;
 import io.ebeaninternal.api.SpiSqlUpdate;
 import io.ebeaninternal.api.SpiTransaction;
 import io.ebeaninternal.api.SpiTransactionManager;
@@ -1585,6 +1586,19 @@ public final class DefaultServer implements SpiServer, SpiEbeanServer {
     }
   }
 
+  @Override
+  public <T> T findSingleAttribute(SpiSqlQuery query, Class<T> cls) {
+
+    RelationalQueryRequest request = new RelationalQueryRequest(this, relationalQueryEngine, query, null);
+    try {
+      request.initTransIfRequired();
+      return request.findSingleAttribute(cls);
+
+    } finally {
+      request.endTransIfRequired();
+    }
+  }
+
   @Override
   public <T> void findDtoEach(SpiDtoQuery<T> query, Consumer<T> consumer) {
     DtoQueryRequest<T> request = new DtoQueryRequest<>(this, dtoQueryEngine, query);

src/main/java/io/ebeaninternal/server/core/RelationalQueryEngine.java

@@ -30,6 +30,11 @@ public interface RelationalQueryEngine {
    */
   void findEach(RelationalQueryRequest request, Predicate<SqlRow> consumer);
 
+  /**
+   * Find single attribute.
+   */
+  <T> T findSingleAttribute(RelationalQueryRequest request, Class<T> cls);
+
   /**
    * Collect SQL query execution statistics.
    */

src/main/java/io/ebeaninternal/server/core/RelationalQueryRequest.java

@@ -53,6 +53,10 @@ public final class RelationalQueryRequest extends AbstractSqlQueryRequest {
     }
   }
 
+  public <T> T findSingleAttribute(Class<T> cls) {
+    return queryEngine.findSingleAttribute(this, cls);
+  }
+
   public void findEach(Consumer<SqlRow> consumer) {
     queryEngine.findEach(this, consumer);
   }
@@ -104,4 +108,11 @@ public final class RelationalQueryRequest extends AbstractSqlQueryRequest {
     }
   }
 
+  public ResultSet getResultSet() {
+    return resultSet;
+  }
+
+  public void incrementRows() {
+    rows++;
+  }
 }

src/main/java/io/ebeaninternal/server/persist/Binder.java

@@ -8,6 +8,8 @@ import io.ebeaninternal.server.core.timezone.DataTimeZone;
 import io.ebeaninternal.server.expression.platform.DbExpressionHandler;
 import io.ebeaninternal.server.persist.platform.MultiValueBind;
 import io.ebeaninternal.server.type.DataBind;
+import io.ebeaninternal.server.type.DataReader;
+import io.ebeaninternal.server.type.RsetDataReader;
 import io.ebeaninternal.server.type.ScalarType;
 import io.ebeaninternal.server.type.TypeManager;
 import org.slf4j.Logger;
@@ -18,6 +20,7 @@ import java.math.BigDecimal;
 import java.sql.CallableStatement;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
+import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Types;
 import java.util.ArrayList;
@@ -196,7 +199,7 @@ public class Binder {
     }
   }
 
-  private ScalarType<?> getScalarType(Class<?> clazz) {
+  public ScalarType<?> getScalarType(Class<?> clazz) {
     ScalarType<?> type = typeManager.getScalarType(clazz);
     if (type == null) {
       throw new PersistenceException("No ScalarType registered for " + clazz);
@@ -457,4 +460,8 @@ public class Binder {
   public DataBind dataBind(PreparedStatement stmt, Connection connection) {
     return new DataBind(dataTimeZone, stmt, connection);
   }
+
+  public DataReader createDataReader(ResultSet resultSet) {
+    return new RsetDataReader(dataTimeZone, resultSet);
+  }
 }

src/main/java/io/ebeaninternal/server/query/DefaultRelationalQueryEngine.java

@@ -10,6 +10,7 @@ import io.ebeaninternal.server.core.Message;
 import io.ebeaninternal.server.core.RelationalQueryEngine;
 import io.ebeaninternal.server.core.RelationalQueryRequest;
 import io.ebeaninternal.server.persist.Binder;
+import io.ebeaninternal.server.type.ScalarType;
 
 import javax.persistence.PersistenceException;
 import java.sql.SQLException;
@@ -91,6 +92,35 @@ public class DefaultRelationalQueryEngine implements RelationalQueryEngine {
     }
   }
 
+  @SuppressWarnings("unchecked")
+  @Override
+  public <T> T findSingleAttribute(RelationalQueryRequest request, Class<T> cls) {
+
+    ScalarType<T> scalarType = (ScalarType<T>) binder.getScalarType(cls);
+    return findScalar(request, scalarType);
+  }
+
+  private <T> T findScalar(RelationalQueryRequest request, ScalarType<T> scalarType) {
+    try {
+      request.executeSql(binder, SpiQuery.Type.ATTRIBUTE);
+
+      T value = null;
+      if (request.next()) {
+        request.incrementRows();
+        value = scalarType.read(binder.createDataReader(request.getResultSet()));
+      }
+
+      request.logSummary();
+      return value;
+
+    } catch (Exception e) {
+      throw new PersistenceException(Message.msg("fetch.error", e.getMessage(), request.getSql()), e);
+
+    } finally {
+      request.close();
+    }
+  }
+
   @Override
   public List<SqlRow> findList(RelationalQueryRequest request) {
 

src/main/java/io/ebeaninternal/server/querydefn/DefaultRelationalQuery.java

@@ -1,8 +1,8 @@
 package io.ebeaninternal.server.querydefn;
 
-import io.ebean.EbeanServer;
 import io.ebean.SqlRow;
 import io.ebeaninternal.api.BindParams;
+import io.ebeaninternal.api.SpiEbeanServer;
 import io.ebeaninternal.api.SpiSqlQuery;
 
 import java.util.List;
@@ -17,7 +17,7 @@ public class DefaultRelationalQuery implements SpiSqlQuery {
 
   private static final long serialVersionUID = -1098305779779591068L;
 
-  private final transient EbeanServer server;
+  private final transient SpiEbeanServer server;
 
   private String label;
 
@@ -39,16 +39,11 @@ public class DefaultRelationalQuery implements SpiSqlQuery {
   /**
    * Additional supply a query detail object.
    */
-  public DefaultRelationalQuery(EbeanServer server, String query) {
+  public DefaultRelationalQuery(SpiEbeanServer server, String query) {
     this.server = server;
     this.query = query;
   }
 
-  public DefaultRelationalQuery setQuery(String query) {
-    this.query = query;
-    return this;
-  }
-
   @Override
   public void findEach(Consumer<SqlRow> consumer) {
     server.findEach(this, consumer, null);
@@ -64,6 +59,11 @@ public class DefaultRelationalQuery implements SpiSqlQuery {
     return server.findList(this, null);
   }
 
+  @Override
+  public <T> T findSingleAttribute(Class<T> cls) {
+    return server.findSingleAttribute(this, cls);
+  }
+
   @Override
   public SqlRow findOne() {
     return server.findOne(this, null);

src/main/java/io/ebeaninternal/server/type/ScalarTypeBigDecimal.java

@@ -32,7 +32,6 @@ public class ScalarTypeBigDecimal extends ScalarTypeBase<BigDecimal> {
 
   @Override
   public BigDecimal read(DataReader dataReader) throws SQLException {
-
     return dataReader.getBigDecimal();
   }