LINQ的可选参数 [英] Linq optional parameters

问题描述

我有一个LINQ查询。我有一大堆的从一种形式我收集的参数，我需要过滤器的基础领域，用户正在搜索的。

I have a linq query. I have a bunch of parameters from a form I collect where I need to filter based of fields the user is searching for.

IQueyable<Users> user = from user in edmxObject.Users
where user.FirstName.Contains(model.FirstName ?? user.FirstName)
&& user.UserName.Contains(model.UserName ?? user.UserName)

我有一些更多的非字符串字段筛选我需要过滤，包括长和布尔。它们可能是空，如果用户没有选择任何东西。我如何将它们包括在查询中。

I have a few more non string field filters I need to filter including long and boolean. They could be nulls if the user does not select anything. How do I include them in the query.

推荐答案

这就是为什么LINQ是如此强大，一个最好的例子 - 延迟执行。你可以建立在不同阶段的查询，并且只有当最后执行或解决将SQL语句来产生查询：

This is one of the best examples of why LINQ is so powerful - deferred execution. You can build up the query in different phases, and only when the query is finally executed or resolved will the SQL statement be generated:

var query = edmxObject.Users.AsQueryable<Users>();

if (! String.IsNullOrEmpty(model.FirstName)) {
    query = from user in query
            where user.FirstName.Contains(model.FirstName)
            select user;
}
if (! String.IsNullOrEmpty(model.UserName) {
    query = from user in query
            where user.UserName.Contains(model.UserName)
            select user;
}

// this will cause the query to execute get the materialized results
var result = query.ToList();

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