Add SelectDistinct() fields overload

Author: mythz

src/ServiceStack.OrmLite/Expressions/SqlExpression.cs

@@ -111,7 +111,7 @@ public virtual SqlExpression<T> Select()
         /// set the specified selectExpression.
         /// </summary>
         /// <param name='selectExpression'>
-        /// raw Select expression: "Select SomeField1, SomeField2 from SomeTable"
+        /// raw Select expression: "SomeField1, SomeField2 from SomeTable"
         /// </param>
         public virtual SqlExpression<T> Select(string selectExpression)
         {
@@ -120,15 +120,30 @@ public virtual SqlExpression<T> Select(string selectExpression)
             return UnsafeSelect(selectExpression);
         }
 
-        public virtual SqlExpression<T> UnsafeSelect(string rawSelect)
+        /// <summary>
+        /// set the specified DISTINCT selectExpression.
+        /// </summary>
+        /// <param name='selectExpression'>
+        /// raw Select expression: "SomeField1, SomeField2 from SomeTable"
+        /// </param>
+        public virtual SqlExpression<T> SelectDistinct(string selectExpression)
+        {
+            selectExpression?.SqlVerifyFragment();
+
+            return UnsafeSelect(selectExpression, distinct:true);
+        }
+
+        public virtual SqlExpression<T> UnsafeSelect(string rawSelect) => UnsafeSelect(rawSelect, distinct: false);
+
+        public virtual SqlExpression<T> UnsafeSelect(string rawSelect, bool distinct)
         {
             if (string.IsNullOrEmpty(rawSelect))
             {
-                BuildSelectExpression(string.Empty, false);
+                BuildSelectExpression(string.Empty, distinct: distinct);
             }
             else
             {
-                this.selectExpression = "SELECT " + rawSelect;
+                this.selectExpression = "SELECT " + (distinct ? "DISTINCT " : "") + rawSelect;
                 this.CustomSelect = true;
                 OnlyFields = null;
             }
@@ -141,7 +156,17 @@ public virtual SqlExpression<T> UnsafeSelect(string rawSelect)
         /// <param name='fields'>
         /// Matching Fields: "SomeField1, SomeField2"
         /// </param>
-        public virtual SqlExpression<T> Select(string[] fields)
+        public virtual SqlExpression<T> Select(string[] fields) => Select(fields, distinct: false);
+
+        /// <summary>
+        /// Set the specified DISTINCT selectExpression using matching fields.
+        /// </summary>
+        /// <param name='fields'>
+        /// Matching Fields: "SomeField1, SomeField2"
+        /// </param>
+        public virtual SqlExpression<T> SelectDistinct(string[] fields) => Select(fields, distinct: true);
+
+        internal virtual SqlExpression<T> Select(string[] fields, bool distinct)
         {
             if (fields == null || fields.Length == 0)
                 return Select(string.Empty);
@@ -192,7 +217,7 @@ public virtual SqlExpression<T> Select(string[] fields)
                 sb.Append(qualifiedName);
             }
 
-            UnsafeSelect(StringBuilderCache.ReturnAndFree(sb));
+            UnsafeSelect(StringBuilderCache.ReturnAndFree(sb), distinct:distinct);
             OnlyFields = new HashSet<string>(fieldsList, StringComparer.OrdinalIgnoreCase);
 
             return this;

tests/ServiceStack.OrmLite.Tests/AutoQueryTests.cs

@@ -463,6 +463,27 @@ public void Can_group_by_multiple_columns()
             }
         }
 
+        [Test]
+        public void Can_query_Rockstars_with_Distinct_Fields()
+        {
+            using (var db = OpenDbConnection())
+            {
+                db.DropAndCreateTable<Rockstar>();
+                db.InsertAll(SeedRockstars);
+                //Add another Michael Rockstar
+                db.Insert(new Rockstar { Id = 8, FirstName = "Michael", LastName = "Bolton", Age = 64, LivingStatus = LivingStatus.Alive, DateOfBirth = new DateTime(1953,02,26) });
+
+                var q = db.From<Rockstar>();
+                q.SelectDistinct(new[]{ "FirstName" });
+
+                var results = db.LoadSelect(q, include:q.OnlyFields);
+
+                results.PrintDump();
+                Assert.That(results.All(x => x.Id == 0));
+                Assert.That(results.Count(x => x.FirstName == "Michael"), Is.EqualTo(1));
+            }
+        }
+
     }
 
 }