如何在 Linq To Sql 查询中重用 where 子句

问题描述

我有用户搜索记录类型的记录.他们在文本框中键入搜索词，然后我通过将多个字段与搜索词匹配来搜索记录.

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.

我的查询看起来像:

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;

我有许多查询都使用相同的过滤器，因此我想提取过滤器以便可以重复使用.类似的东西:

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，它不起作用，因为:

However, it does not work because:

方法System.Object DynamicInvoke(System.Object[])"不支持转换为 SQL.

如何在查询中重复使用我的 where 条件?

How can I reuse my where condition across queries?

推荐答案

使用 编译查询！

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:存储和重用查询.

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