Add support for Sql.CountDistinct()

Author: mythz

src/ServiceStack.OrmLite.Sqlite/SqliteExpression.cs

@@ -62,6 +62,9 @@ protected override object VisitSqlMethodCall(MethodCallExpression m)
                         quotedColName,
                         args.Count == 1 ? string.Format(",{0}", args[0]) : "");
                     break;
+                case "CountDistinct":
+                    statement = string.Format("COUNT(DISTINCT {0})", quotedColName);
+                    break;
                 default:
                     throw new NotSupportedException();
             }

src/ServiceStack.OrmLite/Expressions/Sql.cs

@@ -63,6 +63,11 @@ public static T Count<T>(T value)
             return value;
         }
 
+        public static T CountDistinct<T>(T value)
+        {
+            return value;
+        }
+
         public static string Count(string value)
         {
             return "COUNT({0})".Fmt(value);

src/ServiceStack.OrmLite/Expressions/SqlExpression.cs

@@ -1814,6 +1814,9 @@ protected virtual object VisitSqlMethodCall(MethodCallExpression m)
                         quotedColName,
                         args.Count == 1 ? string.Format(",{0}", args[0]) : "");
                     break;
+                case "CountDistinct":
+                    statement = string.Format("COUNT(DISTINCT {0})", quotedColName);
+                    break;
                 default:
                     throw new NotSupportedException();
             }

tests/ServiceStack.OrmLite.Tests/CustomSqlTests.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Linq;
 using NUnit.Framework;
 using ServiceStack.DataAnnotations;
+using ServiceStack.OrmLite.Tests.Expression;
 using ServiceStack.Text;
 
 namespace ServiceStack.OrmLite.Tests
@@ -203,5 +205,30 @@ public void Can_select_custom_field_expressions()
                 Assert.That(row.Area, Is.EqualTo(10 * 5));
             }
         }
+
+        [Test]
+        public void Can_Count_Distinct()
+        {
+            using (var db = OpenDbConnection())
+            {
+                db.DropAndCreateTable<LetterFrequency>();
+
+                var rows = "A,B,B,C,C,C,D,D,E".Split(',').Map(x => new LetterFrequency { Letter = x });
+
+                db.InsertAll(rows);
+
+                var count = db.Count(db.From<LetterFrequency>().Select(x => x.Letter));
+                Assert.That(count, Is.EqualTo(rows.Count));
+
+                count = db.Scalar<long>(db.From<LetterFrequency>().Select(x => Sql.Count(x.Letter)));
+                Assert.That(count, Is.EqualTo(rows.Count));
+
+                var distinctCount = db.Scalar<long>(db.From<LetterFrequency>().Select(x => Sql.CountDistinct(x.Letter)));
+                Assert.That(distinctCount, Is.EqualTo(rows.Map(x => x.Letter).Distinct().Count()));
+
+                distinctCount = db.Scalar<long>(db.From<LetterFrequency>().Select("COUNT(DISTINCT Letter)"));
+                Assert.That(distinctCount, Is.EqualTo(rows.Map(x => x.Letter).Distinct().Count()));
+            }
+        }
     }
 }