Add new APIs for db.ColumnLazy

Author: mythz

src/ServiceStack.OrmLite/OrmLiteReadConnectionExtensions.cs

@@ -238,6 +238,24 @@ public static List<T> Column<T>(this IDbConnection dbConn, ISqlExpression query)
             return dbConn.Exec(dbCmd => dbCmd.Column<T>(query.ToSelectStatement()));
         }
 
+        /// <summary>
+        /// Returns the first column in a List using a SqlFormat query. E.g:
+        /// <para>db.ColumnLazy&lt;string&gt;("SELECT LastName FROM Person WHERE Age = @age", new { age = 27 })</para>
+        /// </summary>
+        public static IEnumerable<T> ColumnLazy<T>(this IDbConnection dbConn, string sql, object anonType = null)
+        {
+            return dbConn.ExecLazy(dbCmd => dbCmd.ColumnLazy<T>(sql, anonType));
+        }
+
+        /// <summary>
+        /// Returns the distinct first column values in a HashSet using an SqlExpression. E.g:
+        /// <para>db.ColumnLazy&lt;int&gt;(db.From&lt;Persion&gt;().Select(x => x.LastName).Where(q => q.Age == 27))</para>
+        /// </summary>
+        public static IEnumerable<T> ColumnLazy<T>(this IDbConnection dbConn, ISqlExpression query)
+        {
+            return dbConn.ExecLazy(dbCmd => dbCmd.ColumnLazy<T>(query.ToSelectStatement()));
+        }
+
         /// <summary>
         /// Returns the first column in a List using a SqlFormat query. E.g:
         /// <para>db.Column&lt;string&gt;("SELECT LastName FROM Person WHERE Age = @age", new { age = 27 })</para>

src/ServiceStack.OrmLite/OrmLiteReadExtensions.cs

@@ -479,6 +479,34 @@ internal static IEnumerable<T> SelectLazy<T>(this IDbCommand dbCmd, string sql,
             }
         }
 
+        internal static IEnumerable<T> ColumnLazy<T>(this IDbCommand dbCmd, string sql, object anonType = null)
+        {
+            if (anonType != null) dbCmd.SetParameters<T>(anonType, excludeDefaults: false);
+            var dialectProvider = OrmLiteConfig.DialectProvider;
+            dbCmd.CommandText = dialectProvider.ToSelectStatement(typeof(T), sql);
+
+            if (OrmLiteConfig.ResultsFilter != null)
+            {
+                foreach (var item in OrmLiteConfig.ResultsFilter.GetColumn<T>(dbCmd))
+                {
+                    yield return item;
+                }
+                yield break;
+            }
+
+            using (var reader = dbCmd.ExecuteReader())
+            {
+                while (reader.Read())
+                {
+                    var value = dialectProvider.ConvertDbValue(reader.GetValue(0), typeof(T));
+                    if (value == DBNull.Value)
+                        yield return default(T);
+                    else
+                        yield return (T)value;
+                }
+            }
+        }
+
         internal static IEnumerable<T> WhereLazy<T>(this IDbCommand dbCmd, object anonType)
         {
             dbCmd.SetFilters<T>(anonType);

tests/ServiceStack.OrmLite.Tests/OrmLiteSelectTests.cs

@@ -148,6 +148,28 @@ public void Can_loop_each_string_from_ModelWithOnlyStringFields_table()
 			}
 		}
 
+        [Test]
+        public void Can_loop_each_string_from_ModelWithOnlyStringFields_table_Column()
+        {
+            using (var db = OpenDbConnection())
+            {
+                db.DropAndCreateTable<ModelWithOnlyStringFields>();
+
+                var rowIds = new List<string>(new[] { "id-1", "id-2", "id-3" });
+
+                rowIds.ForEach(x => db.Insert(ModelWithOnlyStringFields.Create(x)));
+
+                var dbRowIds = new List<string>();
+                foreach (var rowId in db.ColumnLazy<string>(
+                    db.From<ModelWithOnlyStringFields>().Select(x => x.Id)))
+                {
+                    dbRowIds.Add(rowId);
+                }
+
+                Assert.That(dbRowIds, Is.EquivalentTo(rowIds));
+            }
+        }
+
 		[Test]
 		public void Can_loop_each_with_filter_from_ModelWithOnlyStringFields_table()
 		{