Cannot convert type 'System.Threading.Tasks.Task<System.Data.Common.DbDataReader>' to 'System.Threading.Tasks.Task<System.Data.IDataReader>'

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英文:

Cannot convert type 'System.Threading.Tasks.Task<System.Data.Common.DbDataReader>' to 'System.Threading.Tasks.Task<System.Data.IDataReader>'

问题

  1. 在C#中,我遇到了以下代码的一些问题。

    问题1:我有一个异步方法,执行SQL查询并返回一个Task<IDataReader>,但是当尝试返回另一个异步方法调用的结果时,它会在编译时出错,该方法返回一个Task<System.Data.Common.DbDataReader>。

    代码片段如下:

    public Task&lt;IDataReader&gt; ExecuteReaderAsync(string? sql, object? param = null, IDbTransaction? transaction = null, int? commandTimeout = null, CommandType? commandType = null, CancellationToken? cancellationToken = null)
        =&gt; ExecuteWithResiliency((s, p, c) =&gt; c.ExecuteReaderAsync(s, p, transaction, commandTimeout, commandType), sql, param);
    
    private async Task&lt;T&gt; ExecuteWithResiliency&lt;T&gt;(Func&lt;string, object, SqlConnection, Task&lt;T&gt;&gt; connectionFunc, string sql, object param = null, [CallerMemberName] string operation = &quot;&quot;)
    {
        return await _resiliencyPolicy.ExecuteAsync(
            ctx =&gt; connectionFunc(sql, param, (SqlConnection)_connection),
            ContextHelper.NewContext((SqlConnection)_connection, _logger, sql, param, operation));
    }
    

    问题出现在ExecuteReaderAsync方法中,我在其中尝试调用ExecuteWithResiliency方法来执行SQL查询并返回Task<IDataReader>。然而,它报以下错误:

    无法隐式转换类型'System.Threading.Tasks.Task&lt;System.Data.Common.DbDataReader&gt;'为'System.Threading.Tasks.Task&lt;System.Data.IDataReader&gt;'。
    

    我理解ExecuteWithResiliency方法设计为泛型方法,允许与返回不同类型的异步方法一起工作。然而,似乎System.Data.Common.DbDataReader和System.Data.IDataReader之间存在不兼容性。

    我该如何修改代码以解决此问题,同时保留ExecuteWithResiliency方法的泛型特性?

  2. 无法将'Dapper.CommandDefinition?'转换为'string'

    public async Task&lt;IReadOnlyList&lt;T&gt;&gt; QueryAsync&lt;T&gt;(CommandDefinition? command, CancellationToken? cancellationToken = null) 
        =&gt; (await ExecuteWithResiliency((s, p, c) =&gt; c.QueryAsync&lt;T&gt;(command))).AsList();
    

    对于如何处理这种情况,是否有任何见解或建议将不胜感激。

    请问有人可以在这里提供指导吗?

英文:

I am facing couple of issues with the following code in C#.

  1. I have an asynchronous method that executes a SQL query and returns a Task<IDataReader>, but it gives a compile-time error when trying to return the result of another asynchronous method call that returns a Task<System.Data.Common.DbDataReader>.

The code snippet is as follows:

public Task&lt;IDataReader&gt; ExecuteReaderAsync(string? sql, object? param = null, IDbTransaction? transaction = null, int? commandTimeout = null, CommandType? commandType = null, CancellationToken? cancellationToken = null)
    =&gt; ExecuteWithResiliency((s, p, c) =&gt; c.ExecuteReaderAsync(s, p, transaction, commandTimeout, commandType), sql, param);    

private async Task&lt;T&gt; ExecuteWithResiliency&lt;T&gt;(Func&lt;string, object, SqlConnection, Task&lt;T&gt;&gt; connectionFunc, string sql, object param = null, [CallerMemberName] string operation = &quot;&quot;)
{
    return await _resiliencyPolicy.ExecuteAsync(
        ctx =&gt; connectionFunc(sql, param, (SqlConnection)_connection),
        ContextHelper.NewContext((SqlConnection)_connection, _logger, sql, param, operation));
}

The issue arises in the ExecuteReaderAsync method, where I am trying to call the ExecuteWithResiliency method to execute the SQL query and return a Task<IDataReader>. However, it gives the following error:

Cannot implicitly convert type &#39;System.Threading.Tasks.Task&lt;System.Data.Common.DbDataReader&gt;&#39; to &#39;System.Threading.Tasks.Task&lt;System.Data.IDataReader&gt;&#39;.

I understand that the ExecuteWithResiliency method is designed to be generic, which allows it to work with various asynchronous methods returning different types. However, it seems that there is an incompatibility between System.Data.Common.DbDataReader and System.Data.IDataReader.

How can I modify the code to resolve this issue and make it work correctly while still retaining the generic nature of the ExecuteWithResiliency method?

  1. Cannot convert from 'Dapper.CommandDefinition?' to 'string'

public async Task<IReadOnlyList<T>> QueryAsync<T>(CommandDefinition? command, CancellationToken? cancellationToken = null) => (await ExecuteWithResiliency((s, p, c) => c.QueryAsync<T>(command))).AsList();

Any insights or suggestions on how to handle this situation would be highly appreciated.

Can anyone please help me here by providing their guidance

答案1

得分: 2

System.Data.Common.DbDataReaderSystem.Data.IDataReader,因此您只需 await ExecuteWithResiliency

public async Task<IDataReader> ExecuteReaderAsync(string? sql, object? param = null, IDbTransaction? transaction = null, int? commandTimeout = null, CommandType? commandType = null, CancellationToken? cancellationToken = null)
    => await ExecuteWithResiliency((s, p, c) => c.ExecuteReaderAsync(s, p, transaction, commandTimeout, commandType), sql, param);
英文:

System.Data.Common.DbDataReader is System.Data.IDataReader so you can just await the ExecuteWithResiliency:

public async Task&lt;IDataReader&gt; ExecuteReaderAsync(string? sql, object? param = null, IDbTransaction? transaction = null, int? commandTimeout = null, CommandType? commandType = null, CancellationToken? cancellationToken = null)
    =&gt; await ExecuteWithResiliency((s, p, c) =&gt; c.ExecuteReaderAsync(s, p, transaction, commandTimeout, commandType), sql, param);    

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  • 本文由 发表于 2023年7月28日 02:13:22
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