LINQ to Entities:涉及扩展方法的Orderby语句 [英] LINQ to Entities: Orderby statement involving extension method

问题描述

我正在为网站构建一个简单的搜索功能.目的是允许用户使用鲍勃法杖"之类的查询找到游泳者"并将其通过搜索框添加到列表中.

I'm constructing a simple search function for a site. The aim is to allow the user to find 'swimmers' and add them to a list via a search box, using a query like "bob staff".

我决定解决的第一部分是允许用户通过组名进行搜索(在数据库中，所有游泳者都是组的一部分).以下是我目前拥有的代码.

The first part of this I decided to tackle was allowing the user to search via a group name (In the database all swimmers are part of a group). The following is the code I have at the moment.

[HttpGet]
    public JsonResult searchForSwimmers(string q)
    {
        //designed to return [{name='foo',id='bar'}]

        String[] QueryTerms = q.Split(' '); //all the search terms are sep. by " "
        var groupResults = _db.SwimGroups.Where(g => g.Name.ContainsAny(QueryTerms)) 
            .OrderByDescending(g => g.Name.StartsWithAny(QueryTerms) ? 1 : 0)
            .ThenBy( g => g)
            .Select(g => new { name = g.Name, id = g.ID });


        return Json(groupResults,JsonRequestBehavior.AllowGet);
    }

在第8行，调用了一个名为 StartsWithAny 的方法.这是我在以下文件中定义的扩展方法:

On line 8, there is a method invoked called StartsWithAny. This is an extension method I defined in the following file:

public static class StringUtils
    {
     public static Boolean StartsWithAny(this String str, params String[] Fragments)
        {
            foreach (String fragment in Fragments)
            {
                if (str.StartsWith(fragment))
                {
                    return true;
                }
            }
            return false;
        }
    }

该想法是，如果名称以术语之一开头，则其相关性应排名更高.我认识到这种逻辑是幼稚的并且有缺陷，但是我认为这将是一个很好的例子来说明我所遇到的问题.但是，当在我的cshtml页面中使用以下命令调用searchForSimmers时，代码将进行编译:(使用tokenInput库)

The idea is that if a Name starts with one of the terms then it should be ranked higher in relevancy. I recognize that this logic is naïve and has flaws however I thought it would be a good example to illustrate the problem I've having. The code compiles however when searchForSimmers is invoked in my cshtml page with the following: (using the tokenInput library)

<script type="text/javascript">
     $(document).ready(function () {
          $("#demo-input-local").tokenInput("/Admin/searchForSwimmers");
     });
</script>

我收到500个内部服务器错误.错误消息如下:

I get a 500 internal server error. The error message is as follows:

LINQ to Entities does not recognize the method 'Boolean ContainsAny(System.String, System.String[])' method, and this method cannot be translated into a store expression.

ContainsAny方法

public static Boolean ContainsAny(this String str, List<String> Fragments)
        {
            foreach (String fragment in Fragments)
            {
                if(str.Contains(fragment))
                {
                    return true;
                }
            }
            return false;
        }

我环顾四周，但找不到解决问题的方法.任何帮助将不胜感激，欢呼.

I've had a look around but couldn't find a solution to the problem. Any help would be greatly appreciated, cheers.

推荐答案

在我的博客中创建IQueryable的搜索扩展方法.

Check out my blog where I create a search extension method for IQueryable.

更新:我创建了一个新的博客文章，其中显示了实现您的目标所需的扩展方法

http://www .ninjanye.co.uk/2013/04/generic-iqueryable-or-search-for.html

http://jnye.co/Posts/8/generic-iqueryable-or-search-for-multiple-search-terms-using-expression-trees

问题是linq不知道如何将代码转换为SQL.

The problem is linq does not know how to translate your code into SQL.

通过添加以下扩展方法:

By adding the following extension method:

public static class QueryableExtensions
{
    public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> stringProperty, params string[] searchTerms)
    {
        if (!searchTerms.Any())
        {
            return source;
        }

        Expression orExpression = null;
        foreach (var searchTerm in searchTerms)
        {
            //Create expression to represent x.[property].Contains(searchTerm)
            var searchTermExpression = Expression.Constant(searchTerm);
            var containsExpression = BuildContainsExpression(stringProperty, searchTermExpression);

            orExpression = BuildOrExpression(orExpression, containsExpression);
        }

        var completeExpression = Expression.Lambda<Func<T, bool>>(orExpression, stringProperty.Parameters);
        return source.Where(completeExpression);
    }

    private static Expression BuildOrExpression(Expression existingExpression, Expression expressionToAdd)
    {
        if (existingExpression == null)
        {
            return expressionToAdd;
        }

        //Build 'OR' expression for each property
        return Expression.OrElse(existingExpression, expressionToAdd);
    }

    private static MethodCallExpression BuildContainsExpression<T>(Expression<Func<T, string>> stringProperty, ConstantExpression searchTermExpression)
    {
        return Expression.Call(stringProperty.Body, typeof(string).GetMethod("Contains"), searchTermExpression);
    }

}

这将允许您编写以下lambda:

This will allow you to write the following lambda:

[HttpGet]
public JsonResult searchForSwimmers(string q)
{
    //designed to return [{name='foo',id='bar'}]

    String[] QueryTerms = q.Split(' '); //all the search terms are sep. by " "
    var groupResults = _db.SwimGroups.Search(g => g.Name, queryTerms) 
                                     .OrderByDescending(g => g.Name.StartsWithAny(QueryTerms) ? 1 : 0)
                                     .ThenBy( g => g)
                                     .Select(g => new { name = g.Name, id = g.ID });

    return Json(groupResults,JsonRequestBehavior.AllowGet);
}    

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