如何将字符串解析为UNIQUEIDENTIFIER? [英] How can I parse a string into a UNIQUEIDENTIFIER?

问题描述

我正在编写一个Entity Framework LINQ查询，其中我想将字符串解析为UNIQUEIDENTIFIER(aka GUID)作为 WHERE 子句的一部分:

I'm writing an Entity Framework LINQ query in which I want to parse a string into a UNIQUEIDENTIFIER (aka GUID) as part of the WHERE clause:

public IEnumerable<User> Find(Guid guid)
{
    return dbContext
        .Users
        .Where(user => Guid.Parse(user.GuidText) == guid);
}

我知道这在SQL中是可能的，因为我已经对其进行了测试:

I know this is possible in SQL because I've tested it:

SELECT *
FROM Users
WHERE CAST(GuidText AS UNIQUEIDENTIFIER) = @guid;

但是，我还没有找到生成 CAST 部分的方法.我尝试过:

However, I haven't found a way to generate the CAST part. I've tried:

1. (Guid)user.GuidText ，它会生成编译器错误.
2. Convert.ToGuid(user.GuidText)，但此方法不存在.
3. Guid.Parse(user.GuidText)，但这会导致Entity Framework在转换LINQ查询时生成错误.
4. 新Guid(user.GuidText)，但这会导致Entity Framework在转换LINQ查询时生成错误.
5. (Guid)Convert.ChangeType(user.GuidText，typeof(Guid))，但这会导致Entity Framework在转换LINQ查询时生成错误.
6. SqlGuid.Parse(user.GuidText)，但这会导致Entity Framework在转换LINQ查询时生成错误.

1. (Guid)user.GuidText, which generates a compiler error.
2. Convert.ToGuid(user.GuidText), but this method doesn't exist.
3. Guid.Parse(user.GuidText), but this causes Entity Framework to generate an error when it translates the LINQ query.
4. new Guid(user.GuidText), but this causes Entity Framework to generate an error when it translates the LINQ query.
5. (Guid)Convert.ChangeType(user.GuidText, typeof(Guid)), but this causes Entity Framework to generate an error when it translates the LINQ query.
6. SqlGuid.Parse(user.GuidText), but this causes Entity Framework to generate an error when it translates the LINQ query.

我该如何实现?我愿意在最后的方法中将SQL嵌入代码中.

How can I achieve this? I'm willing to embed SQL in the code as a last resort.

推荐答案

EF运行时实际上支持将字符串转换为GUID作为强制转换操作，但是正如您所发现的那样，目前我们无法在LINQ中表达这一点.支持.

EF runtime actually supports converting from a string to a GUID as a cast operation, but as you find out there is currently no way of expressing this in LINQ that we support.

我能想到的最好的解决方法是使用Entity SQL:

The best workaround that I can think of is to use Entity SQL:

var objectContext = ((IObjectContextAdapter)db).ObjectContext;
var query = objectContext.CreateQuery<User>(
  "SELECT VALUE u FROM Context.Users AS u WHERE CAST(u.GuidText AS System.Guid) = @guid", 
  new ObjectParameter("guid", guid));

这篇关于如何将字符串解析为UNIQUEIDENTIFIER?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！