在Dapper中管理与非缓冲查询的连接

Question

我最近开始使用 短小精悍, ，一切似乎都很好，很容易，但有一件事一直让我困惑:连接管理。

根据 文件:

Dapper并不管理连接的生命周期，它假定 它得到的连接是开放的，没有现有的datareaders枚举 （除非火星启用）

有鉴于此，我开始在我的存储库方法的实现中这样做:

using (var db = new SqliteConnection(connectionString)) {
    // call Dapper methods here
}

然后我遇到了一个有大量记录的表，所以我想返回一个 IEnumerable<T> 通过传递 buffered: false 向 Query<> 方法，当我开始在前端枚举枚举枚举时，出现一个异常，说连接已关闭并被处置，这是预期的，因为我正在用前面的using块包装我的调用。

问题: 解决这个问题的最佳方法？
侧面问题: 我管理连接的方式是首选的方式吗？

Answer 1

我会提供这个存储库模式:

public class Repository
{
    private readonly string _connectionString;

    public Repository(string connectionString)
    {
        _connectionString = connectionString;
    }

    protected T GetConnection<T>(Func<IDbConnection, T> getData)
    {
        using (var connection = new SqlConnection(_connectionString))
        {
            connection.Open();
            return getData(connection);
        }
    }

    protected TResult GetConnection<TRead, TResult>(Func<IDbConnection, TRead> getData, Func<TRead, TResult> process)
    {
        using (var connection = new SqlConnection(_connectionString))
        {
            connection.Open();
            var data = getData(connection);
            return process(data);
        }
    }
}

对于缓冲查询，您希望使用第一个重载 GetConnection 方法，对于非缓冲您使用第二，指定回调处理数据:

public class MyRepository : Repository
{
    public MyRepository(string connectionString) : base(connectionString)
    {
    }

    public IEnumerable<MyMapObject> GetData()
    {
        return GetConnection(c => c.Query<MyMapObject>(query));
    }

    public IEnumerable<ResultObject> GetLotsOfData(Func<IEnumerable<MyMapObject>, IEnumerable<ResultObject>> process)
    {
        return GetConnection(c => c.Query<MyMapObject>(query, buffered: false), process);
    }
}

非常基本的用法:

static void Main(string[] args)
{
    var repository = new MyRepository(connectionString);
    var data = repository.GetLotsOfData(ProcessData);
}

public static IEnumerable<ResultObject> ProcessData(IEnumerable<MyMapObject> data)
{
    foreach (var record in data)
    {
        var result = new ResultObject();
        //do some work...
        yield return result;
    }
}

但请记住-在这种情况下，连接可能会打开太长时间。..

Answer 2

@sergio，太棒了！谢谢你的这种伟大模式。我将其修改为异步，以便我可以使用Dapper的异步方法。使我的整个请求链异步，从控制器一直回到db！华丽！

public abstract class BaseRepository
{
    private readonly string _ConnectionString;

    protected BaseRepository(string connectionString)
    {
        _ConnectionString = connectionString;
    }

    // use for buffered queries
    protected async Task<T> WithConnection<T>(Func<IDbConnection, Task<T>> getData)
    {
        try
        {
            using (var connection = new SqlConnection(_ConnectionString))
            {
                await connection.OpenAsync();
                return await getData(connection);
            }
        }
        catch (TimeoutException ex)
        {
            throw new Exception(String.Format("{0}.WithConnection() experienced a SQL timeout", GetType().FullName), ex);
        }
        catch (SqlException ex)
        {
            throw new Exception(String.Format("{0}.WithConnection() experienced a SQL exception (not a timeout)", GetType().FullName), ex);
        }
    }

    // use for non-buffeed queries
    protected async Task<TResult> WithConnection<TRead, TResult>(Func<IDbConnection, Task<TRead>> getData, Func<TRead, Task<TResult>> process)
    {
        try
        {
            using (var connection = new SqlConnection(_ConnectionString))
            {
                await connection.OpenAsync();
                var data = await getData(connection);
                return await process(data);
            }
        }
        catch (TimeoutException ex)
        {
            throw new Exception(String.Format("{0}.WithConnection() experienced a SQL timeout", GetType().FullName), ex);
        }
        catch (SqlException ex)
        {
            throw new Exception(String.Format("{0}.WithConnection() experienced a SQL exception (not a timeout)", GetType().FullName), ex);
        }
    }
}

.

与如此如此：

public class PersonRepository : BaseRepository
{
    public PersonRepository(string connectionString): base (connectionString) { }

    // Assumes you have a Person table in your DB that 
    // aligns with a Person POCO model.
    //
    // Assumes you have an existing SQL sproc in your DB 
    // with @Id UNIQUEIDENTIFIER as a parameter. The sproc 
    // returns rows from the Person table.
    public async Task<Person> GetPersonById(Guid Id)
    {
        return await WithConnection(async c =>
        {
            var p = new DynamicParameters();
            p.Add("Id", Id, DbType.Guid);
            var people = await c.QueryAsync<Person>(sql: "sp_Person_GetById", param: p, commandType: CommandType.StoredProcedure);
            return people.FirstOrDefault();
        });
    }
}

.