NEW: FetchCountDistinct - query can return distinct values with their counts (#1300)

* NEW: FetchCountDistinct - query can return distinct values with their counts

* Have to disable asserts, because of #1298

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

@@ -1,5 +1,6 @@
 package io.ebeaninternal.server.query;
 
+import io.ebean.CountDistinctOrder;
 import io.ebean.Query;
 import io.ebean.RawSql;
 import io.ebean.RawSqlBuilder;
@@ -190,7 +191,7 @@ class CQueryBuilder {
     CQueryPlan queryPlan = request.getQueryPlan();
     if (queryPlan != null) {
       predicates.prepare(false);
-      return new CQueryFetchSingleAttribute(request, predicates, queryPlan);
+      return new CQueryFetchSingleAttribute(request, predicates, queryPlan, query.isCountDistinct());
     }
 
     // use RawSql or generated Sql
@@ -201,7 +202,7 @@ class CQueryBuilder {
 
     queryPlan = new CQueryPlan(request, s.getSql(), sqlTree, false, s.isIncludesRowNumberColumn(), predicates.getLogWhereSql());
     request.putQueryPlan(queryPlan);
-    return new CQueryFetchSingleAttribute(request, predicates, queryPlan);
+    return new CQueryFetchSingleAttribute(request, predicates, queryPlan, query.isCountDistinct());
   }
 
   /**
@@ -549,8 +550,13 @@ class CQueryBuilder {
           }
         }
       }
-
-      sb.append(select.getSelectSql());
+      if (query.isCountDistinct() && query.isSingleAttribute()) {
+        sb.append("r1.attribute_, count(*) from (select ");
+        sb.append(select.getSelectSql());
+        sb.append(" as attribute_");
+      } else {
+        sb.append(select.getSelectSql());
+      }
       if (query.isDistinctQuery() && dbOrderBy != null && !query.isSingleAttribute()) {
         // add the orderBy columns to the select clause (due to distinct)
         sb.append(", ").append(DbOrderByTrim.trim(dbOrderBy));
@@ -642,10 +648,15 @@ class CQueryBuilder {
       sb.append(" having ").append(dbHaving);
     }
 
-    if (dbOrderBy != null) {
+    if (dbOrderBy != null && !query.isCountDistinct()) {
       sb.append(" order by ").append(dbOrderBy);
     }
 
+    if (query.isCountDistinct() && query.isSingleAttribute()) {
+      sb.append(") r1 group by r1.attribute_");
+      sb.append(toSql(query.getCountDistinctOrder()));
+    }
+
     if (useSqlLimiter) {
       // use LIMIT/OFFSET, ROW_NUMBER() or rownum type SQL query limitation
       SqlLimitRequest r = new OrmQueryLimitRequest(sb.toString(), dbOrderBy, query, dbPlatform);
@@ -657,6 +668,25 @@ class CQueryBuilder {
 
   }
 
+  private String toSql(CountDistinctOrder orderBy) {
+    switch(orderBy) {
+    case ATTR_ASC:
+      return " order by r1.attribute_";
+    case ATTR_DESC:
+      return " order by r1.attribute_ desc";
+    case COUNT_ASC_ATTR_ASC:
+      return " order by count(*), r1.attribute_";
+    case COUNT_ASC_ATTR_DESC:
+      return " order by count(*), r1.attribute_ desc";
+    case COUNT_DESC_ATTR_ASC:
+      return " order by count(*) desc, r1.attribute_";
+    case COUNT_DESC_ATTR_DESC:
+      return " order by count(*) desc, r1.attribute_ desc";
+    default:
+      throw new IllegalArgumentException("Illegal enum: "+ orderBy);
+    }
+  }
+  
   /**
    * Append where or and based on the hasWhere flag.
    */

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

@@ -1,6 +1,7 @@
 package io.ebeaninternal.server.query;
 
 import io.ebean.util.JdbcClose;
+import io.ebean.CountedValue;
 import io.ebeaninternal.api.SpiProfileTransactionEvent;
 import io.ebeaninternal.api.SpiQuery;
 import io.ebeaninternal.api.SpiTransaction;
@@ -60,18 +61,21 @@ class CQueryFetchSingleAttribute implements SpiProfileTransactionEvent {
 
   private final ScalarType<?> scalarType;
 
+  private final boolean containsCounts;
+
   private long profileOffset;
 
   /**
    * Create the Sql select based on the request.
    */
-  CQueryFetchSingleAttribute(OrmQueryRequest<?> request, CQueryPredicates predicates, CQueryPlan queryPlan) {
+  CQueryFetchSingleAttribute(OrmQueryRequest<?> request, CQueryPredicates predicates, CQueryPlan queryPlan, boolean containsCounts) {
     this.request = request;
     this.queryPlan = queryPlan;
     this.query = request.getQuery();
     this.sql = queryPlan.getSql();
     this.desc = request.getBeanDescriptor();
     this.predicates = predicates;
+    this.containsCounts = containsCounts;
     this.scalarType = queryPlan.getSingleAttributeScalarType();
     query.setGeneratedSql(sql);
   }
@@ -101,7 +105,11 @@ class CQueryFetchSingleAttribute implements SpiProfileTransactionEvent {
 
       List<Object> result = new ArrayList<>();
       while (dataReader.next()) {
-        result.add(scalarType.read(dataReader));
+        Object value = scalarType.read(dataReader);
+        if (containsCounts) {
+          value = new CountedValue<>(value, dataReader.getLong());
+        }
+        result.add(value);
         dataReader.resetColumnPosition();
         rowCount++;
       }

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

@@ -110,7 +110,7 @@ public final class SqlTreeBuilder {
     this.query = request.getQuery();
     this.temporalMode = SpiQuery.TemporalMode.of(query);
     this.disableLazyLoad = query.isDisableLazyLoading();
-    this.subQuery = Type.SUBQUERY == query.getType() || Type.ID_LIST == query.getType();
+    this.subQuery = Type.SUBQUERY == query.getType() || Type.ID_LIST == query.getType() || Type.DELETE == query.getType() || query.isCountDistinct();
     this.includeJoin = query.getM2mIncludeJoin();
     this.manyWhereJoins = query.getManyWhereJoins();
     this.queryDetail = query.getDetail();