c#中的泛型和谓词

Question

我有以下不工作的代码。说明无法解析PartitionKey和RowKey的值。我希望有专家能给我一些建议。到目前为止，我所做的是基于一些建议，但仍然不起作用。

public class BaseTable
{
    public string PartitionKey { get; set; }
    public string RowKey { get; set; }
}
public abstract class AzureTableBase<T> : IAzureTable<T>
    {
     // This method gives the errors. The idea of this method is that instead of 
     // supplying the predicate you can just supply a value for partitionkey and
     // rowkey as parameters. The problem is that it doesn't work and give the 
     // following syntax errors:
     //
     // Cannot resolve symbol PartitionKey
     // Cannot resolve symbol RowKey
     public virtual T Get<T>(string pkey, string rkey) where T : BaseTable
     {
         var a = this.Query.Where(u => u.PartitionKey == pkey && u.RowKey == rkey);
     }
     //  Following method works:
     public virtual T Get(Expression<Func<T, bool>> predicate)
     {
         return this.Query.Where(predicate).FirstOrDefault();
     }
     public virtual IQueryable<T> Query
     {
        get
        {
            TableServiceContext context = CreateContext();
            return context.CreateQuery<T>(TableName).AsTableServiceQuery();
        }
     }
}

下面是我当前如何调用第二个Get函数的示例:

SubTest = testTable.Get(u => u.PartitionKey == "XX" & u.RowKey == "YY")

我想要的是能够像这样命名它:

SubTest = testTable.Get("XX","YY")

Answer 1

如果这是你的确切代码，你不能有自由浮动的函数，你需要把你的Get<T>放在一个类中，一个最好有Query字段的排序。

基于你更新的帖子和你完全拒绝发布一段完整的代码，我只能假设你并不真正关心(甚至不理解)你的代码是做什么的，只关心它能编译。关于这一点，

public abstract class AzureTableBase<T> : IAzureTable<T> where T : BaseTable
{
     // don't need to re-generalize this function, T is already inherited from your class
     public virtual T Get(string pkey, string rkey)
     {
         var a = this.Query.Where(u => u.PartitionKey == pkey && u.RowKey == rkey);
         return a.FirstOrDefault();     // again, only guessing.
     }
     public virtual IQueryable<T> Query
     {
        get
        {
            TableServiceContext context = CreateContext();
            return context.CreateQuery<T>(TableName).AsTableServiceQuery();
        }
     }
}

Answer 2

这将返回某种集合，可能是IQueryable:

this.Query.Where(u => u.PartitionKey == pkey && u.RowKey == rkey);

您的方法声称返回类型为T的值，在这种情况下被约束为BaseTable(或可能是一个子类)。这两种类型不兼容

Answer 3

@ blind是正确的，但是还有一个问题…是否T或类型返回由context.CreateQuery<T>(TableName).AsTableServiceQuery();实际上继承从BaseTable?

例子

class OneOfYourTables : BaseTable
{
}