From 762bd0df2b4334159c35426da1f2423b3af26b76 Mon Sep 17 00:00:00 2001
From: 28810 <28810@YEXIANGQIN>
Date: Thu, 25 Jul 2019 10:11:50 +0800
Subject: [PATCH] =?UTF-8?q?-=20=E4=BF=AE=E5=A4=8D=20ToList=E8=A1=A8?=
 =?UTF-8?q?=E8=BE=BE=E5=BC=8F=E6=9F=A5=E8=AF=A2=E8=B5=8B=E5=80=BCstring.Em?=
 =?UTF-8?q?pty=E5=90=8E=E4=BA=A7=E7=94=9F=E9=94=99=E8=AF=AF=E7=9A=84SQL?=
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 FreeSql.Tests/FreeSql.Tests/UnitTest1.cs | 44 ++++++++++++++++++++----
 FreeSql/Internal/CommonExpression.cs     |  8 ++++-
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/FreeSql.Tests/FreeSql.Tests/UnitTest1.cs b/FreeSql.Tests/FreeSql.Tests/UnitTest1.cs
index fbdda02a..31210d4f 100644
--- a/FreeSql.Tests/FreeSql.Tests/UnitTest1.cs
+++ b/FreeSql.Tests/FreeSql.Tests/UnitTest1.cs
@@ -13,6 +13,19 @@ using System.Collections;
 
 namespace FreeSql.Tests
 {
+    public static class SqlFunc
+    {
+        public static T TryTo<T>(this string that)
+        {
+            return default(T);
+        }
+
+        public static string FormatDateTime()
+        {
+            return "";
+        }
+    }
+
     public class UnitTest1
     {
 
@@ -287,17 +300,32 @@ namespace FreeSql.Tests
             public TaskBuild Parent { get; set; }
         }
 
-        public class SqlFunc
-        {
-            public static string FormatDateTime()
-            {
-                return "";
-            }
-        }
+        
 
+        void parseExp(object sender, Aop.ParseExpressionEventArgs e)
+        {
+            if (e.Expression.NodeType == ExpressionType.Call)
+            {
+                var callExp = e.Expression as MethodCallExpression;
+                if (callExp.Object == null && callExp.Arguments.Any() && callExp.Arguments[0].Type == typeof(string))
+                {
+                    if (callExp.Method.Name == "TryTo")
+                    {
+                        e.Result = Expression.Lambda(
+                            typeof(Func<>).MakeGenericType(callExp.Method.GetGenericArguments().FirstOrDefault()), 
+                            e.Expression).Compile().DynamicInvoke()?.ToString();
+                        return;
+                    }
+                }
+            }
+        } 
         [Fact]
         public void Test1()
         {
+            g.sqlite.Aop.ParseExpression += parseExp;
+
+            var sqddddl = g.sqlite.Select<TaskBuild>().ToSql(t => t.OptionsEntity04 == "1".TryTo<int>());
+
             var sqksdkfjl = g.sqlite.Select<TaskBuild>()
                 .LeftJoin(a => a.Templates.Id2 == a.TemplatesId)
                 .LeftJoin(a => a.Parent.Id == a.Id)
@@ -809,6 +837,8 @@ namespace FreeSql.Tests
             {
                 a.Key.tt2,
                 cou1 = a.Count(),
+                empty = "",
+                nil = (string)null,
                 arg1 = a.Avg(a.Key.mod4),
                 ccc2 = a.Key.tt2 ?? "now()",
                 //ccc = Convert.ToDateTime("now()"), partby = Convert.ToDecimal("sum(num) over(PARTITION BY server_id,os,rid,chn order by id desc)")
diff --git a/FreeSql/Internal/CommonExpression.cs b/FreeSql/Internal/CommonExpression.cs
index cfaf858e..2d7360f5 100644
--- a/FreeSql/Internal/CommonExpression.cs
+++ b/FreeSql/Internal/CommonExpression.cs
@@ -44,7 +44,13 @@ namespace FreeSql.Internal
                     //	ccc = "now()", 
                     //	partby = "sum(num) over(PARTITION BY server_id,os,rid,chn order by id desc)"
                     //})，有缺点即 ccc partby 接受类型都是 string，可配合 Convert.ToXxx 类型转换，请看下面的兼容
-                    parent.DbField = constExp.Type.FullName == "System.String" ? (constExp.Value?.ToString() ?? "NULL") : _common.FormatSql("{0}", constExp?.Value);
+                    if (constExp.Type.FullName == "System.String")
+                    {
+                        var constExpValue = constExp.Value?.ToString() ?? "NULL";
+                        if (constExpValue == string.Empty) constExpValue = _common.FormatSql("{0}", "");
+                        parent.DbField = constExpValue;
+                    } else
+                        parent.DbField = _common.FormatSql("{0}", constExp?.Value);
                     field.Append(", ").Append(parent.DbField);
                     if (index >= 0) field.Append(" as").Append(++index);
                     return false;