使用C＃动态筛选列/属性到EF 4.1查询

我试图在C＃中使用linq创建一个通用的“搜索引擎”。我有一个简单的搜索引擎，其功能和外观如下所示。使用C＃动态筛选列/属性到EF 4.1查询

var query = "joh smi"; 
var searchTerms = query.Split(new char[] { ' ' }); 
var numberOfTerms = searchTerms.Length; 

var matches = from p in this.context.People 
       from t in searchTerms 
       where p.FirstName.Contains(t) || 
       p.LastName.Contains(t) 
       group p by p into g 
       where g.Count() == numberOfTerms 
       select g.Key;

我希望它是更通用的，因此我可以这样调用：

var matches = Search<Person>(dataset, query, p => p.FirstName, p => p.LastName);

据我已经得到了作为追随者，但是它失败了“的LINQ表达式节点类型“调用”在LINQ to Entities中不受支持。“ System.NotSupportedException。

static IEnumerable<T> Find<T>(IQueryable<T> items, string query, 
           params Func<T, string>[] properties) 
{ 
    var terms = query.Split(' '); 
    var numberOfParts = terms.Length; 

    foreach (var prop in properties) 
    { 
     var transformed = items.SelectMany(item => terms, 
       (item, term) => new { term, item }); 

               // crashes due to this method call 
     var filtered = transformed.Where(p => prop(p.item).Contains(p.term)); 
     items = filtered.Select(p => p.item); 
    } 

    return from i in items 
      group i by i into g 
      where g.Count() == numberOfParts 
      select g.Key; 
}

我敢肯定这是可行的，有刚有要编译i => i.FirstName到Expression<Func<T, bool>>的方式，但是这就是我的LINQ的专业知识结束。有没有人有任何想法？

来源

2011-06-27 djeebus

您应该使用谓词生成器来构建你的Or查询，像：

var predicate = PredicateBuilder.False<T>(); 
foreach (var prop in properties) 
{ 
    Func<T, string> currentProp = prop; 
    predicate = predicate.Or (p => currentProp(p.item).Contains(p.term)); 
} 
var result = items.Where(predicate);

来源

2011-06-27 23:48:06 Variant

这仍然不允许LINQ到实体以扩大表达 P => currentProp（p.item ）。载（p.term） – djeebus

考虑使用一个规范模式。检查出this blog。具体来说，看看他开发的规格模式。这与@Variant类似，您可以在其中构建动态规范并将其传递到您的上下文或存储库。

来源

2011-06-28 13:12:53 DDiVita

原来查询的内容只需要'扩展'。我用库发现here来扩展表达式。我认为这允许Linq to Entities将其转换为sql。你会注意到Expand被一次又一次地调用;我认为所有这些都是必要的。无论如何，它工作。代码遵循：

using System.Linq.Expressions; 

public static class SearchEngine<T> 
{ 
    class IandT<T> 
    { 
     public string Term { get; set; } 
     public T Item { get; set; } 
    } 

    public static IEnumerable<T> Find(
        IQueryable<T> items, 
        string query, 
        params Expression<Func<T, string>>[] properties) 
    { 
     var terms = query.Split(new char[] { ' ' }, 
           StringSplitOptions.RemoveEmptyEntries); 
     var numberOfParts = terms.Length; 

     Expression<Func<IandT<T>, bool>> falseCond = a => false; 
     Func<Expression<Func<IandT<T>, bool>>, 
      Expression<Func<IandT<T>, bool>>, 
      Expression<Func<IandT<T>, bool>>> combineOr = 
       (f, g) => (b) => f.Expand(b) || g.Expand(b); 

     var criteria = falseCond; 

     foreach (var prop in properties) 
     { 
      var currentprop = prop; 
      Expression<Func<IandT<T>, bool>> current = c => 
        currentprop.Expand(c.Item).IndexOf(c.Term) != -1; 
      criteria = combineOr(criteria.Expand(), current.Expand()); 
     } 

     return from p in items.ToExpandable() 
       from t in terms 
       where criteria.Expand(new IandT<T> { Item = p, Term = t }) 
       group p by p into g 
       where g.Count() == numberOfParts 
       select g.Key; 
    } 
}

它可以通过下面的代码来调用：

var matches = Search<Person>(dataset, query, p => p.FirstName, p => p.LastName);

来源

2011-07-01 14:06:55 djeebus

使用C＃动态筛选列/属性到EF 4.1查询

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