在LINQ查询中将Int连接为字符串

Question

我有以下LINQ查询。

var providers = from c in Repository.Query<Company>()
                where !c.IsDeleted
                select new { c.Description, Id = "C" + c.Id };

我正在尝试将ID连接到“ C”。 因此，例如，如果c.Id为35，则结果应为“ C35”。

这显然不起作用，因为您不能在字符串中添加整数（ c.Id ）。 我可以使用C.使用string.Format()或转换类型轻松解决此问题。 但是如何在LINQ中做到这一点？

Answer 1

如果仅在准备结果时需要.NET功能（而不是过滤，则应在RDBMS端进行此操作，以避免在内存中带入过多数据），通常的技巧是使用AsEnumerable在内存中完成转换方法：

var providers = Repository.Query<Company>()
    .Where(c => !c.IsDeleted)
    .Select(c => new { c.Description, c.Id }) // <<== Prepare raw data
    .AsEnumerable() // <<== From this point it's LINQ to Object
    .Select(c => new { c.Description, Id = "C"+c.Id }); // <<== Construct end result

Answer 2

尝试使用SqlFunctions.StringConvert Method ：

var xd = (from c in Repository.Query<Company>()
           where !c.IsDeleted
           select new { c.Description, Id = "C" + SqlFunctions.StringConvert((double)c.Id).Trim()});

Answer 3

您编写的代码可以正常工作。 这是相同代码的模型，它输出Id的

class Company
{
    public string Description { get; set; }
    public int Id { get; set; }
    public bool IsDeleted { get; set; }
}

static void Main()
{
    //setup
    var list = new List<Company>();
    list.Add(new Company
    {
        Description = "Test",
        Id = 35,
        IsDeleted = false
    });
    list.Add(new Company
    {
        Description = "Test",
        Id = 52,
        IsDeleted = false
    });
    list.Add(new Company
    {
        Description = "Test",
        Id = 75,
        IsDeleted = true
    });

    /* code you are looking for */
    var providers = from c in list
                    where !c.IsDeleted
                    select new { c.Description, Id = "C" + c.Id };

    foreach (var provider in providers)
    {
        Console.WriteLine(provider.Id);
    }

        Console.ReadKey();
}

Answer 4

字符串格式呢

var providers = from c in Repository.Query<Company>()
                where !c.IsDeleted
                select new { c.Description, Id = "C" + c.Id.ToString() };