在Dapper中管理与非缓冲查询的连接

Question

我最近开始使用Dapper，一切看起来都很好，很简单，但是有一件事让我感到困惑：连接管理。

根据documentation：

Dapper不管理您连接的生命周期，它假定它获得的连接是打开的，并且没有现有的数据读取器枚举（除非启用了MARS）

鉴于此，我开始在我的存储库方法的实现中执行此操作：

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

然后我遇到了一个包含大量记录的表，因此我虽然通过将IEnumerable<T>传递给buffered: false方法来返回Query<>，但是当我开始在前端枚举可枚举对象时，异常，指出连接已关闭并已释放，这是预期的，因为我将调用与前面的using块包装在一起。

问题：解决此问题的最佳方法？旁边的问题：我管理连接的方式是否是首选的方式？

Answer 1

我将提供此存储库模式：

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，您想使用GetConnection方法的第一个重载，对于非缓冲查询，您要使用第二个，指定回调来处理数据：

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;
    }
}

但是请记住-在这种情况下连接可能会打开太长时间...

Answer 2

@@ Sergio，真棒！感谢您的出色模式。我将其稍作修改以使其异步，以便可以将其与Dapper的异步方法一起使用。使我的整个请求链都异步，从控制器一直回到数据库！太棒了！

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);
        }
    }
}

像这样与Dapper一起使用：

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();
        });
    }
}