diff --git a/FreeSql.Tests/UnitTest1.cs b/FreeSql.Tests/UnitTest1.cs
index 9af6083d..4b6c705f 100644
--- a/FreeSql.Tests/UnitTest1.cs
+++ b/FreeSql.Tests/UnitTest1.cs
@@ -123,9 +123,18 @@ namespace FreeSql.Tests {
 			}
 		}
 
+		public class TestEnum {
+			public Guid id { get; set; }
+			public Enum em { get; set; }
+		}
+
 		[Fact]
 		public void Test1() {
 
+			
+			g.sqlite.Insert(new TestEnum { }).ExecuteAffrows();
+			var telist = g.sqlite.Select<TestEnum>().ToList();
+
 			Assert.Throws<Exception>(() => g.sqlite.CodeFirst.SyncStructure<TestEnumable>());
 
 			var TestEnumable = new TestEnumable();
diff --git a/FreeSql/FreeSqlBuilder.cs b/FreeSql/FreeSqlBuilder.cs
index 9ce5494c..9b2d4315 100644
--- a/FreeSql/FreeSqlBuilder.cs
+++ b/FreeSql/FreeSqlBuilder.cs
@@ -103,6 +103,7 @@ namespace FreeSql {
 
 		public IFreeSql Build() => Build<IFreeSql>();
 		public IFreeSql<TMark> Build<TMark>() {
+			if (string.IsNullOrEmpty(_masterConnectionString)) throw new Exception("参数 masterConnectionString 不可为空，请检查 UseConnectionString");
 			IFreeSql<TMark> ret = null;
 			Type type = null;
 			switch(_dataType) {