LINQ到SQL：结合（或运算）多与QUOT;包含＆QUOT;过滤器？ [英] Linq-to-SQL: Combining (OR'ing) multiple "Contains" filters?

问题描述

我有一些麻烦搞清楚做到这一点的最好办法，我就AP preciate任何帮助。

I'm having some trouble figuring out the best way to do this, and I would appreciate any help.

基本上，我设立一个过滤器，允许用户看的与用户名的任意过滤器相关联的审核项的历史。

Basically, I'm setting up a filter that allows the user to look at a history of audit items associated with an arbitrary "filter" of usernames.

数据源是SQL Server数据库，所以我走的是IQueryable的源（无论是从数据库上下文对象，或者是一个IQueryable直接表引用这使我们从其他查询），应用WHERE过滤器，然后返回所产生的IQueryable对象....但我有点难倒就如何执行或使用这种方法。

The datasource is a SQL Server data base, so I'm taking the IQueryable "source" (either a direct table reference from the db context object, or perhaps an IQueryable that's resulted from additional queries), applying the WHERE filter, and then returning the resultant IQueryable object....but I'm a little stumped as to how to perform OR using this approach.

我已经考虑过的前pressions的路线，因为我知道如何还是那些，但我一直没能找出相当如何做到这一点与包含式的评价，所以我米目前使用UNION，但恐怕这可能会对性能造成负面影响，我想知道，如果它不能给我正是我需要的，如果其他过滤器（除用户名的过滤如图所示）的加入一个arbirary订单。

I've considered going the route of Expressions because I know how to OR those, but I haven't been able to figure out quite how to do that with a "Contains" type evaluation, so I'm currently using a UNION, but I'm afraid this might have negative impact on performance, and I'm wondering if it may not give me exactly what I need if other filters (in addition to user name filtering shown here) are added in an arbirary order.

下面是我的示例code：

Here is my sample code:

public override IQueryable<X> ApplyFilter<X>(IQueryable<X> source)
{
    // Take allowed values...
    List<string> searchStrings = new List<string>();

    // <SNIP> (This just populates my list of search strings)

    IQueryable<X> oReturn = null;

    // Step through each iteration, and perform a 'LIKE %value%' query
    string[] searchArray = searchStrings.ToArray();
    for (int i = 0; i < searchArray.Length; i++)
    {
        string value = searchArray[i];
        if (i == 0)
            // For first step, perform direct WHERE
            oReturn = source.Where(x => x.Username.Contains(value));
        else
            // For additional steps, perform UNION on WHERE
            oReturn = oReturn.Union(source.Where(x => x.Username.Contains(value)));
    }
    return oReturn ?? source;
}

这感觉就像是错误的方式做事情，但它似乎工作，所以我的问题是第一次，有没有更好的办法做到这一点？此外，有没有办法做一个'包含'或'像'与前pressions？

This feels like the wrong way to do things, but it does seem to work, so my question is first, is there a better way to do this? Also, is there a way to do a 'Contains' or 'Like' with Expressions?

（Editted改正我的code：在回滚，以便将它张贴在工作状态，我显然没有回退到很远不够:)）

(Editted to correct my code: In rolling back to working state in order to post it, I apparently didn't roll back quite far enough :) )

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ETA：按所给的解决方案，这是我新的code（万一有人读这有兴趣）：

public override IQueryable<X> ApplyFilter<X>(IQueryable<X> source)
{
    List<string> searchStrings = new List<string>(AllowedValues);

    // <SNIP> build collection of search values 

    string[] searchArray = searchStrings.ToArray();

    Expression<Func<X, bool>> expression = PredicateBuilder.False<X>();

    for (int i = 0; i < searchArray.Length; i++)
    {
        string value = searchArray[i];
        expression = expression.Or(x => x.Username.Contains(value));
    }
    return source.Where(expression);
}

（但是要注意一点，我注意到：继predicateBuilder的例子​​中，搜索字符串的一个空的集合将返回false（假||值1 || ...），而在我原来的版本，我是假设一个空​​列表应该只是coallesce到未过滤的源。当我想到了更多的，新的版本似乎更有意义，我的需要，所以我采取了）

(One caveat I noticed: Following the PredicateBuilder's example, an empty collection of search strings will return false (false || value1 || ... ), whereas in my original version, I was assuming an empty list should just coallesce to the unfiltered source. As I thought about it more, the new version seems to make more sense for my needs, so I adopted that)

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推荐答案

您可以使用 predicateBuilder 从LINQkit动态地构造查询。

You can use the PredicateBuilder from the LINQkit to dynamically construct your query.

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