lambda表达式中的实体框架测试长度

Question

我试图编写一个Entity Framework lambda表达式来查找其中字符串字段的长度大于零的记录。 以下代码可以编译，但不会返回我期望的结果：

foreach (CUSTOMER c in (_db.CUSTOMERs.Where<CUSTOMER>(i => i.CUSTPREVIOUSEMAIL.Length > 0)))
{...}

结果返回的一组客户包括CUSTPREVIOUSEMAIL值为空字符串的客户。

为什么不起作用？ 我该如何运作？

这是生成的SQL：

SELECT 
"B"."CUSTID" AS "CUSTID", 
"B"."CUSTFNAME" AS "CUSTFNAME", 
"B"."CUSTLNAME" AS "CUSTLNAME", 
"B"."CUSTADDRESS" AS "CUSTADDRESS", 
"B"."CUSTCITY" AS "CUSTCITY", 
"B"."CUSTSTATE" AS "CUSTSTATE", 
"B"."CUSTZIP" AS "CUSTZIP", 
"B"."CUSTTYPE" AS "CUSTTYPE", 
"B"."CUSTPHONE1" AS "CUSTPHONE1", 
"B"."CUSTPHONE2" AS "CUSTPHONE2", 
"B"."CUSTINTCLASS" AS "CUSTINTCLASS", 
"B"."CUSTSPARE1" AS "CUSTSPARE1", 
"B"."CUSTSPARE2" AS "CUSTSPARE2", 
"B"."CUSTDATE1" AS "CUSTDATE1", 
"B"."CUSTDATE2" AS "CUSTDATE2", 
"B"."CUSTEMAIL" AS "CUSTEMAIL", 
"B"."STOREID" AS "STOREID", 
"B"."CUSTDISCOUNT" AS "CUSTDISCOUNT", 
"B"."CUSTTAXEXEMPT" AS "CUSTTAXEXEMPT", 
"B"."CUSTNOTES" AS "CUSTNOTES", 
"B"."CUSTINACTIVE" AS "CUSTINACTIVE", 
"B"."CUSTBDAY" AS "CUSTBDAY", 
"B"."CUSTBADCHECK" AS "CUSTBADCHECK", 
"B"."CUSTDISOUNTCEXPIRES" AS "CUSTDISOUNTCEXPIRES", 
"B"."CUSTTERMS" AS "CUSTTERMS", 
"B"."CUSTPRICELEVEL" AS "CUSTPRICELEVEL", 
"B"."CUSTCREDITLIMIT" AS "CUSTCREDITLIMIT", 
"B"."CUSTTOTALMONEY" AS "CUSTTOTALMONEY", 
"B"."CUSTTOTALVOLUME" AS "CUSTTOTALVOLUME", 
"B"."CUSTTAXEXEMPT2" AS "CUSTTAXEXEMPT2", 
"B"."CUSTTAXEXEMPT3" AS "CUSTTAXEXEMPT3", 
"B"."CUSTPOPUPNOTES" AS "CUSTPOPUPNOTES", 
"B"."CUSTCOMPANY" AS "CUSTCOMPANY", 
"B"."CUSTCOUNTRY" AS "CUSTCOUNTRY", 
"B"."CUSTKEY" AS "CUSTKEY", 
"B"."CUSTTIMESTAMP" AS "CUSTTIMESTAMP", 
"B"."CUSTREFCODE" AS "CUSTREFCODE", 
"B"."CUSTSPARECHECK2" AS "CUSTSPARECHECK2", 
"B"."CUSTSPARECHECK3" AS "CUSTSPARECHECK3", 
"B"."CUSTSPARECHECK4" AS "CUSTSPARECHECK4", 
"B"."CUSTSPARECHECK5" AS "CUSTSPARECHECK5", 
"B"."CUSTTAXCODE" AS "CUSTTAXCODE", 
"B"."CUSTEMAILUPDATED" AS "CUSTEMAILUPDATED", 
"B"."CUSTPHONE3" AS "CUSTPHONE3", 
"B"."CUSTOPTOUT" AS "CUSTOPTOUT", 
"B"."CUSTLASTSYNCED" AS "CUSTLASTSYNCED", 
"B"."CUSTPREVIOUSEMAIL" AS "CUSTPREVIOUSEMAIL"
FROM "CUSTOMER" AS "B"
WHERE (CHAR_LENGTH("B"."CUSTPREVIOUSEMAIL")) > 0

Answer 1

我认为您必须检查null而不是0。试试这个foreach（（_db.CUSTOMERs.Where（i => i.CUSTPREVIOUSEMAIL.ToLower（）！=“ null”）中的C客户）{...}