如何从字符串创建 LINQ 查询? [英] How to create LINQ Query from string?

问题描述

我是 LINQ 的新手，真的需要一些编码方面的帮助.

I am new at LINQ and really need a help with some coding.

目前，我有一个字符串和一个 var 变量.

At the moment, I have a string and a var variables.

string temp = "from product in myEntities.Products where product.Name.Contains(_Name) select product";
var _Products = temp;
LvProducts.DataSource = _Products;
LvProducts.DataBind();

基本上，我想要做的是能够通过预先将其分配到字符串中来创建自定义/复杂的 LINQ 查询.完成组合后，我将字符串分配给 var 变量.然而，这显然是行不通的.因此，有人可以帮助我吗?

Basically, what I want to do is to be able to create a custom/complicated LINQ query by assigning it into a string beforehand. After done with composing, I assign the string into the var variable. However, this is obviously will not work. Therefore, can anyone assist me on this?

推荐答案

您有几个选择:

• 使用Dynamic Linq用于构建查询的库苍蝇.最好的地方开始是通过阅读 ScottGu 的博客输入.然而，我不认为这些库支持包含你的例子中的方法.这里一篇解释如何添加的博客文章这种支持.

• Use the the Dynamic Linq libraries to construct you queries on the fly. The best place to get started is by reading ScottGu's blog entry. However, I don't think these libraries support the contains method in your example. Here is a blog post explaining how to add this support.

直接执行 SQL 语句.查看 Linq to Sql 或 Linq 到实体.

Directly execute SQL statements. Check out the MSDN docs for Linq to Sql or Linq to Entities.

var _Products = myEntities.ExecuteStoreQuery<Product>
(@"SELECT * FROM Products WHERE [Name] In ('Item1', 'Item2')");

使用 Linq 的可组合行为.这可能不是最优雅的解决方案，但如果您没有太多选择，它会非常有效.您可以只构建多个部分的查询.

Use Linq's composable behaviour. This might not be the most elegant solution but it works really well if you do not have too many options. You can just construct your query in multiple parts.

var _Products = from product in myEntities.Products
                select product

_Products = from product in _Products 
            where product.Name.Contains(_Name)
            select product

if FilterByPrice {
    _Products = from product in _Products 
                where product.Price > 100 
                select product
}

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