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FrameWork/SqlSugar/ExpressionsToSql/CaseWhen/CaseWhen.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+
+namespace SqlSugar
+{
+    public class CaseWhen
+    {
+        public CaseThen ElseIF(bool condition)
+        {
+            return null;
+        }
+        public T End<T>(T defaultValue)
+        {
+            return default(T);
+        }
+    }
+    public class CaseThen
+    {
+
+        public CaseWhen Return<T>(T result)
+        {
+            return null;
+        }
+    }
+}

FrameWork/SqlSugar/ExpressionsToSql/CaseWhen/CaseWhenResolve.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+
+namespace SqlSugar
+{
+
+    public class CaseWhenResolve
+    {
+        List<MethodCallExpression> allMethods = new List<MethodCallExpression>();
+        private ExpressionContext context = null;
+        public CaseWhenResolve(MethodCallExpression expression, ExpressionContext context, Expression oppsiteExpression)
+        {
+            this.context = context;
+            var currentExpression = expression;
+            allMethods.Add(currentExpression);
+            if (context.IsSingle && oppsiteExpression != null&& oppsiteExpression is MemberExpression)
+            {
+                var childExpression = (oppsiteExpression as MemberExpression).Expression;
+                this.context.SingleTableNameSubqueryShortName = (childExpression as ParameterExpression).Name;
+            }
+            else if (context.IsSingle)
+            {
+                this.context.SingleTableNameSubqueryShortName = (context.Expression as LambdaExpression).Parameters.First().Name;
+            }
+            while (currentExpression != null)
+            {
+                var addItem = currentExpression.Object as MethodCallExpression;
+                if (addItem != null)
+                    allMethods.Add(addItem);
+                currentExpression = addItem;
+            }
+        }
+
+        public string GetSql()
+        {
+            allMethods.Reverse();
+            List<KeyValuePair<string, string>> sqls = new List<KeyValuePair<string, string>>();
+            foreach (var methodExp in allMethods)
+            {
+                var isFirst = allMethods.First() == methodExp;
+                var isLast= allMethods.Last() == methodExp;
+                var sql= SubTools.GetMethodValue(this.context, methodExp.Arguments[0],this.context.IsSingle?ResolveExpressType.WhereSingle:ResolveExpressType.WhereMultiple);
+                sqls.Add(new KeyValuePair<string, string>(methodExp.Method.Name, sql));
+            }
+            var result= this.context.DbMehtods.CaseWhen(sqls);
+            return result;
+        }
+    }
+}