通用LINQ查询predicate？ [英] Generic LINQ query predicate?

问题描述

不知道这是可能的，或者如果我的前pressing我正在寻找正确的东西，但我有下面这段code在我的图书馆反复想练习一些干。 我已经设置基于ALA谷歌一个简单的用户提供的搜索字段，我查询的SQL Server表。我使用LINQ基于什么是在搜索字符串组成最终的查询。我正在寻找一种方式来使用泛型和lambda函数通过创建可重用常规出这样的：

Not sure if this is possible or if I'm expressing correctly what I'm looking for, but I have the following piece of code in my library repeatedly and would like to practice some DRY. I have set of SQL Server tables that I'm querying based on a simple user-supplied search field ala Google. I'm using LINQ to compose the final query based on what's in the search string. I'm looking for a way to use generics and passed in lambda functions to create a reusable routine out of this:

string[] arrayOfQueryTerms = getsTheArray();

var somequery = from q in dataContext.MyTable
                select q;

if (arrayOfQueryTerms.Length == 1)
{
    somequery = somequery.Where<MyTableEntity>(
        e => e.FieldName.StartsWith(arrayOfQueryTerms[0]));
}
else
{
    foreach(string queryTerm in arrayOfQueryTerms)
    {
        if (!String.IsNullOrEmpty(queryTerm))
        {
            somequery = somequery 
                        .Where<MyTableEntity>(
                            e => e.FieldName.Contains(queryTerm));
        }
    }
}

我希望创建一个通用的方法，有特色，看起来是这样的：

I was hoping to create a generic method with signature that looks something like:

private IQueryable<T> getQuery(
    T MyTableEntity, string[] arrayOfQueryTerms, Func<T, bool> predicate)

我用所有我的表相同的搜索策略，让真正的不同使用情况，使用的唯一的事情就是MyTable的＆放大器; MyTableEntity搜索和字段名搜索。这是否有意义？有没有使用LINQ的方式来动态传递领域的where子句中查询这个名字？或者，我可以通过在此为predicate拉姆达？

I'm using the same search strategy across all my tables, so the only thing that really differs from usage to usage is the MyTable & MyTableEntity searched and the FieldName searched. Does this make sense? Is there a way with LINQ to dynamically pass in the name of the field to query in the where clause? Or can I pass in this as a predicate lambda?

e => e.FieldName.Contains(queryTerm)

我知道有一百万个半方法可以做到这在SQL中，可能更容易，但我很想把一切都在LINQ家庭为这一个。另外，我觉得仿制药应为这样的问题是很方便。任何想法？

I realize there a million and a half ways to do this in SQL, probably easier, but I'd love to keep everything in the LINQ family for this one. Also, I feel that generics should be handy for a problem like this. Any ideas?

推荐答案

这听起来像你正在寻找动态的LINQ。看看<一href="http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx"相对=nofollow>此处。这使您可以传递字符串作为参数的查询方法，如：

It sounds like you're looking for Dynamic Linq. Take a look here. This allows you to pass strings as arguments to the query methods, like:

var query = dataSource.Where("CategoryID == 2 && UnitPrice > 3")
                      .OrderBy("SupplierID");

编辑：另一组关于这一问题的帖子，用C＃4的动态支持：的第1部分和的第2部分。

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