[英]Conversion between IEnumerable to IList (Dapper return result)
There is signature of UserManager
method (ASP .NET Identity Core default implementation): 有UserManager
方法的签名(ASP .NET Identity Core默认实现):
public Task<IList<string>> GetRolesAsync(User user) {
const string query = @"
select r.[Name]
from [UserRoles] ur
left join [Roles] r on r.RoleId = ur.RoleId
where ur.UserId = @userId;
";
return Task.Factory.StartNew(() => {
using (SqlConnection connection = new SqlConnection(_connectionString))
return connection.Query<string>(query, new { userId = user.UserId });
});
}
But unfortunately Dapper.Query<T>
returns IEnumerable<T>
. 但不幸的是, Dapper.Query<T>
返回IEnumerable<T>
。
Is it possible to return IList<T>
or i have to make conversion myself? 是否可以返回IList<T>
或者我必须自己进行转换?
Dapper only guarantees to hand you an IEnumerable<T>
. Dapper只保证向您提供IEnumerable<T>
。 So you should only assume that. 所以你应该只假设这一点。 In particular, it already has different scenarios where it can give you either a populated list, or a deferred iterator. 特别是,它已经拥有了不同的场景中它可以给你无论是填充的列表, 或延期迭代器。
The simplest approach is to just call .ToList()
. 最简单的方法是调用.ToList()
。 If you are intent on avoiding an alloc, then maybe do a speculative test: 如果您打算避免使用alloc,那么可以进行推测测试:
static IList<T> SpeculativeToList<T>(this IEnumerable<T> source)
{
return source as IList<T> ?? source.ToList();
}
Just call .ToList()
on it? 只需调用.ToList()
就可以了吗?
return connection.Query<string>(query, new { userId = user.UserId }).ToList();
This would enumerate the IEnumerable<T>
and create an in-memory copy of all elements found as a List<T>
. 这将枚举IEnumerable<T>
并创建作为List<T>
找到的所有元素的内存中副本。
尝试使用显式强制转换
return (IList<string>)connection.Query<string>(query, new { userId = user.UserId });
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