Fix select distinct lob fields with db2

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanProperty.java

@@ -1160,7 +1160,11 @@ public class BeanProperty implements ElPropertyValue, Property, STreeProperty {
   public boolean isLob() {
     return lob;
   }
-
+  
+  public boolean isDbLob() {
+    return lob || dbType == DbPlatformType.JSON && dbLength == 0;
+  }
+  
   public static boolean isLobType(int type) {
     switch (type) {
       case Types.CLOB:

ebean-core/src/main/java/io/ebeaninternal/server/deploy/DynamicPropertyAggregationFormula.java

@@ -62,4 +62,9 @@ class DynamicPropertyAggregationFormula extends DynamicPropertyBase {
     ctx.appendParseSelect(parsedFormula, alias);
   }
 
+  @Override
+  public boolean isDbLob() {
+    return false;
+  }
+
 }

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

@@ -752,6 +752,10 @@ final class CQueryBuilder {
     return dbPlatform.isPlatform(Platform.POSTGRES);
   }
 
+  boolean isPlatformDistinctNoLobs() {
+    return dbPlatform.isPlatform(Platform.DB2); // CHECKME: Also oracle?
+  }
+
   /**
    * Return the 'for update' FROM hint (sql server).
    */

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

@@ -28,6 +28,11 @@ public interface STreeProperty extends ScalarDataReader<Object> {
    * Return true if the property is the Id.
    */
   boolean isId();
+  
+  /**
+   * Returns true, if this is a lob property.
+   */
+  boolean isDbLob();
 
   /**
    * Return true if the property is an embedded type.

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

@@ -35,6 +35,7 @@ public final class SqlTreeBuilder {
   private final CQueryPredicates predicates;
   private final boolean subQuery;
   private final boolean distinctOnPlatform;
+  private final boolean distinctNoLobs;
   /**
    * Property if resultSet contains master and detail rows.
    */
@@ -65,6 +66,7 @@ public final class SqlTreeBuilder {
     this.query = null;
     this.subQuery = false;
     this.distinctOnPlatform = false;
+    this.distinctNoLobs = false;
     this.queryDetail = queryDetail;
     this.predicates = predicates;
     this.temporalMode = SpiQuery.TemporalMode.CURRENT;
@@ -97,6 +99,7 @@ public final class SqlTreeBuilder {
     this.predicates = predicates;
     this.alias = new SqlTreeAlias(request.baseTableAlias(), temporalMode);
     this.distinctOnPlatform = builder.isPlatformDistinctOn();
+    this.distinctNoLobs = builder.isPlatformDistinctNoLobs();
     String fromForUpdate = builder.fromForUpdate(query);
     CQueryHistorySupport historySupport = builder.getHistorySupport(query);
     CQueryDraftSupport draftSupport = builder.getDraftSupport(query);
@@ -266,6 +269,9 @@ public final class SqlTreeBuilder {
     if (joinList != null) {
       joinList.add(selectNode);
     }
+    if (sqlDistinct && distinctNoLobs) {
+      selectNode.unselectLobs();
+    }
     return selectNode;
   }
 

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

@@ -92,4 +92,9 @@ interface SqlTreeNode {
    * Add dependent tables to the given set.
    */
   void dependentTables(Set<String> tables);
+
+  /**
+   * Unselect lobs (for distinct queries on DB2 and Oracle).
+   */
+  default void unselectLobs() {};
 }

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

@@ -4,7 +4,9 @@ import io.ebean.bean.BeanCollection;
 import io.ebean.bean.EntityBean;
 import io.ebean.bean.EntityBeanIntercept;
 import io.ebean.bean.PersistenceContext;
+import io.ebean.core.type.DataReader;
 import io.ebean.core.type.ScalarDataReader;
+import io.ebean.core.type.ScalarType;
 import io.ebean.util.SplitName;
 import io.ebeaninternal.api.SpiQuery;
 import io.ebeaninternal.api.SpiQuery.Mode;
@@ -15,6 +17,7 @@ import io.ebeaninternal.server.deploy.TableJoin;
 import io.ebeaninternal.server.deploy.id.IdBinder;
 
 import java.sql.SQLException;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -36,8 +39,8 @@ class SqlTreeNodeBean implements SqlTreeNode {
   /**
    * Set to true if this is a partial object fetch.
    */
-  private final boolean partialObject;
-  private final STreeProperty[] properties;
+  private boolean partialObject;
+  private STreeProperty[] properties;
   /**
    * Extra where clause added by Where annotation on associated many.
    */
@@ -700,4 +703,32 @@ class SqlTreeNodeBean implements SqlTreeNode {
     }
     return false;
   }
+  
+  @Override
+  public void unselectLobs() {
+    if (children != null) {
+      for (SqlTreeNode child : children) {
+        child.unselectLobs();
+      }
+    }
+    if (hasLob()) {
+      List<STreeProperty> lst = new ArrayList<>();
+      for (STreeProperty prop : properties) {
+        if (!prop.isDbLob()) {
+          lst.add(prop);
+        }
+      }
+      properties = lst.toArray(new STreeProperty[0]);
+      partialObject = true;
+    }
+  }
+  
+  private boolean hasLob() {
+    for (STreeProperty prop : properties) {
+      if (prop.isDbLob()) {
+        return true;
+      }
+    }
+    return false;
+  }
 }