如何重用哪里Linq中的条款SQL查询 [英] How to reuse where clauses in Linq To Sql queries

问题描述

我有搜索的用户类型为Record的记录。他们键入搜索词中的一个文本框，然后我通过与搜索词匹配多个领域的搜索记录。

I have users searching records of type Record. They type a search term in a textbox and then I search records by matching several fields with the search term.

我的查询是这样的：

var results = from record in DataContext.Records
              where
                   record.Field1.ToLower().Contains(term) ||
                   record.Field2.ToLower().Contains(term) ||
                   record.Field3.ToLower().Contains(term)
              select record;

我有一个数字，都使用相同的过滤器的查询，因此我想提取滤波，因此它可以被重复使用。是这样的：

I have a number of queries that all use the same filter and thus I would like to extract the filtering so it can be reused. Something like:

var filter = new Func<Record, string, bool>(
                (record, term) =>
                    record.Field1.ToLower().Contains(term) ||
                    record.Field2.ToLower().Contains(term) ||
                    record.Field3.ToLower().Contains(term)
             );

var results = from record in DataContext.Records
              where filter(record, term)
              select record;

然而，这是行不通的，因为：

However, it does not work because:

法System.Object的DynamicInvoke（System.Object的[]）没有支持转换为SQL。

如何重用我在这里穿过查询条件？

How can I reuse my where condition across queries?

推荐答案

使用一个<一个href="http://msdn.microsoft.com/en-us/library/system.data.linq.compiledquery.aspx">CompiledQuery!

var filter = CompiledQuery.Compile(
    (DatabaseDataContext dc, Record record, string term) =>
        record.Field1.ToLower().Contains(term) ||
        record.Field2.ToLower().Contains(term) ||
        record.Field3.ToLower().Contains(term)
);

var results = from record in DataContext.Records
              where filter(DataContext, record, term)
              select record;

有关详细信息，请参阅如何：储存和再利用查询

For more information, see How to: Store and Reuse Queries.

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