- 优化 表达式中不能使用 c# 函数的问题，

> 如：where(a => HttpContext.Session.GetString("UserID") == a.UserId)

FreeSql/Extensions/LambadaExpressionExtensions.cs

@@ -86,6 +86,13 @@ namespace System.Linq.Expressions
             var body = Expression.Not(exp.Body);
             return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
         }
+
+        internal static bool IsParameter(this Expression exp)
+        {
+            var test = new TextParameterExpressionVisitor();
+            test.Visit(exp);
+            return test.Result;
+        }
     }
 
     internal class NewExpressionVisitor : ExpressionVisitor
@@ -102,4 +109,15 @@ namespace System.Linq.Expressions
         protected override Expression VisitParameter(ParameterExpression node) =>
             node == _oldParameter ? this._newParameter : node;
     }
+
+    internal class TextParameterExpressionVisitor : ExpressionVisitor
+    {
+        public bool Result { get; private set; }
+
+        protected override Expression VisitParameter(ParameterExpression node)
+        {
+            if (!Result) Result = true;
+            return node;
+        }
+    }
 }