Refactor internals add SqlTreeRoot as follow up to #2179

Adds SqlTreeRoot interface to make it more explicit that SqlTreeNodeRoot is the only valid top level node in the sql tree (and as such has the root level load() method)

ebean-core/src/main/java/io/ebeaninternal/server/query/CQuery.java

@@ -142,7 +142,7 @@ public class CQuery<T> implements DbReadContext, CancelableQuery, SpiProfileTran
    * Tree that knows how to build the master and detail beans from the
    * resultSet.
    */
-  private final SqlTreeNode rootNode;
+  private final SqlTreeRoot rootNode;
 
   /**
    * For master detail query.
@@ -444,13 +444,13 @@ public class CQuery<T> implements DbReadContext, CancelableQuery, SpiProfileTran
     if (manyProperty == null) {
       // only single resultSet row required to build object so we are done
       // read a single resultSet row into single bean
-      nextBean = rootNode.load(this, null, null);
+      nextBean = rootNode.load(this);
       return true;
     }
 
     if (nextBean == null) {
       // very first read
-      nextBean = rootNode.load(this, null, null);
+      nextBean = rootNode.load(this);
     } else {
       // nextBean set to previously read currentBean
       nextBean = currentBean;
@@ -478,7 +478,7 @@ public class CQuery<T> implements DbReadContext, CancelableQuery, SpiProfileTran
    * is different to the nextBean (false if we need to read more rows).
    */
   private boolean checkForDifferentBean() throws SQLException {
-    currentBean = rootNode.load(this, null, null);
+    currentBean = rootNode.load(this);
     return currentBean != nextBean;
   }
 

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTree.java

@@ -122,8 +122,8 @@ class SqlTree {
     return inheritanceWhereSql;
   }
 
-  SqlTreeNode getRootNode() {
-    return rootNode;
+  SqlTreeRoot getRootNode() {
+    return (SqlTreeRoot)rootNode;
   }
 
   /**

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNode.java

@@ -73,11 +73,6 @@ interface SqlTreeNode {
    */
   EntityBean load(DbReadContext ctx, EntityBean localBean, EntityBean contextBean) throws SQLException;
 
-  /**
-   * Load a version of a @History bean with effective dates.
-   */
-  <T> Version<T> loadVersion(DbReadContext ctx) throws SQLException;
-
   /**
    * Return true if the query has a many join.
    */

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNodeBean.java

@@ -192,20 +192,6 @@ class SqlTreeNodeBean implements SqlTreeNode {
     }
   }
 
-  /**
-   * Read the version bean.
-   */
-  @Override
-  @SuppressWarnings("unchecked")
-  public <T> Version<T> loadVersion(DbReadContext ctx) throws SQLException {
-    // read the sys period lower and upper bounds
-    // these are always the first 2 columns in the resultSet
-    Timestamp start = ctx.getDataReader().getTimestamp();
-    Timestamp end = ctx.getDataReader().getTimestamp();
-    T bean = (T) load(ctx, null, null);
-    return new Version<>(bean, start, end);
-  }
-
   /**
    * Load that takes into account inheritance.
    */

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNodeExtraJoin.java

@@ -178,14 +178,6 @@ class SqlTreeNodeExtraJoin implements SqlTreeNode {
     return null;
   }
 
-  /**
-   * Does nothing.
-   */
-  @Override
-  public <T> Version<T> loadVersion(DbReadContext ctx) {
-    return null;
-  }
-
   @Override
   public boolean hasMany() {
     return manyJoin;

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNodeFormulaWhereJoin.java

@@ -99,12 +99,6 @@ class SqlTreeNodeFormulaWhereJoin implements SqlTreeNode {
     return null;
   }
 
-  @Override
-  public <T> Version<T> loadVersion(DbReadContext ctx) {
-    // nothing to do here
-    return null;
-  }
-
   @Override
   public boolean hasMany() {
     return true;

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNodeManyWhereJoin.java

@@ -144,12 +144,6 @@ class SqlTreeNodeManyWhereJoin implements SqlTreeNode {
     return null;
   }
 
-  @Override
-  public <T> Version<T> loadVersion(DbReadContext ctx) {
-    // nothing to do here
-    return null;
-  }
-
   @Override
   public boolean hasMany() {
     return true;

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeNodeRoot.java

@@ -1,16 +1,21 @@
 package io.ebeaninternal.server.query;
 
+import io.ebean.Version;
+import io.ebean.bean.EntityBean;
 import io.ebeaninternal.api.SpiQuery;
+import io.ebeaninternal.server.deploy.DbReadContext;
 import io.ebeaninternal.server.deploy.DbSqlContext;
 import io.ebeaninternal.server.deploy.TableJoin;
 
+import java.sql.SQLException;
+import java.sql.Timestamp;
 import java.util.List;
 import java.util.Set;
 
 /**
  * Represents the root node of the Sql Tree.
  */
-final class SqlTreeNodeRoot extends SqlTreeNodeBean {
+final class SqlTreeNodeRoot extends SqlTreeNodeBean implements SqlTreeRoot {
 
   private final TableJoin includeJoin;
 
@@ -35,6 +40,25 @@ final class SqlTreeNodeRoot extends SqlTreeNodeBean {
     return true;
   }
 
+  @Override
+  public EntityBean load(DbReadContext ctx) throws SQLException {
+    return load(ctx, null, null);
+  }
+
+  /**
+   * Read the version bean.
+   */
+  @Override
+  @SuppressWarnings("unchecked")
+  public <T> Version<T> loadVersion(DbReadContext ctx) throws SQLException {
+    // read the sys period lower and upper bounds
+    // these are always the first 2 columns in the resultSet
+    Timestamp start = ctx.getDataReader().getTimestamp();
+    Timestamp end = ctx.getDataReader().getTimestamp();
+    T bean = (T) load(ctx, null, null);
+    return new Version<>(bean, start, end);
+  }
+
   @Override
   public boolean isSqlDistinct() {
     return sqlDistinct;

ebean-core/src/main/java/io/ebeaninternal/server/query/SqlTreeRoot.java

@@ -0,0 +1,34 @@
+package io.ebeaninternal.server.query;
+
+import io.ebean.Version;
+import io.ebean.bean.EntityBean;
+import io.ebean.core.type.ScalarDataReader;
+import io.ebeaninternal.server.deploy.DbReadContext;
+
+import java.sql.SQLException;
+
+/**
+ * The root level node of the SqlTree.
+ */
+interface SqlTreeRoot {
+
+  /**
+   * Load the bean from the DbReadContext.
+   * <p>
+   * At a high level this actually controls the reading of the data from the
+   * jdbc resultSet and putting it into the bean etc.
+   * </p>
+   */
+  EntityBean load(DbReadContext ctx) throws SQLException;
+
+  /**
+   * Load a version of a @History bean with effective dates.
+   */
+  <T> Version<T> loadVersion(DbReadContext ctx) throws SQLException;
+
+  /**
+   * Return a Scalar single attribute reader based on the first property.
+   */
+  ScalarDataReader<?> getSingleAttributeReader();
+
+}