LINQ to Entities:为什么不能使用Split方法作为条件? [英] LINQ to Entities: Why can't I use Split method as condition?

问题描述

我有以下LINQ查询:

I have the following LINQ query:

var aKeyword = "ACT";
var results = from a in db.Activities
              where a.Keywords.Split(',').Contains(aKeyword) == true
              select a;

关键字是一个逗号分隔的字段.

Keywords is a comma delimited field.

每次我运行此查询时，都会出现以下错误:

Everytime I run this query I get the following error:

"LINQ to Entities无法识别方法'Boolean Contains [String](System.Collections.Generic.IEnumerable`1 [System.String]，System.String)'方法，并且该方法无法转换进入商店表达式."

我要做什么呢?

推荐答案

针对大数据集上的性能考量:

In response to your performance considerations on a big dataset:

您将要在客户端上进行非索引通配符字符串匹配，因此，是的，会导致性能下降.

You are going to be doing non indexed wildcard string matching on the client, so yes, there will be performance loss.

在一个表字段中有多个关键字是有原因的吗?您可以将其归一化，以创建一个ActivityKeywords表，其中每个Activity都有许多Keyword记录.

Is there a reason why you have multiple keywords in one table field? You could normalize that out, to have a ActivityKeywords table where for each Activity you have a number of Keyword records.

活动(activity_id，.../*删除关键字字段*/)---> ActivityKeywords(活动ID，keyword_id)--->关键字(keyword_id，值)

Activities(activity_id, ... /* remove keywords field */) ---> ActivityKeywords(activity_id, keyword_id) ---> Keywords(keyword_id, value)

检出非第一范式: http://en.wikipedia.org/wiki/Database_normalization

同样，即使您只坚持一栏，也有一种方法可以在服务器端执行所有操作(如果您使用严格的语法:'keyword1，keyword2，...，keywordN'):

Also even if you were to stick with the one column, there is a way to do everything serverside (if you have a strict syntax: 'keyword1, keyword2, ..., keywordN'):

var aKeyword = "ACT";
var results = (from a in db.Activities
              where a.Keywords.Contains("," + aKeyword) || a.Keywords.Contains(aKeyword + ",")
              select a;

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