我一直在玩Dapper，但我不确定处理数据库连接的最佳方法。
大多数示例显示在示例类中创建的连接对象，甚至在每个方法中。但是我觉得在每个clss中引用连接字符串都是错误的，即使它是从web.config中提取的。
我的经验是使用DbDataContext或DbContext与Linq to SQL或Entity Framework，所以这对我来说是新的。
使用Dapper作为我的数据访问策略时，如何构建我的Web应用程序？
答案 0 :(得分：23)
我使用从配置中检索连接字符串的属性创建了扩展方法。这使得调用者不必知道关于连接的任何信息，无论是打开还是关闭等等。这个方法确实限制了你，因为你隐藏了一些Dapper功能，但在我们相当简单的应用程序中，它对我们来说很好用如果我们需要Dapper的更多功能，我们总是可以添加一个新的扩展方法来公开它。
internal static string ConnectionString = new Configuration().ConnectionString;
internal static IEnumerable<T> Query<T>(string sql, object param = null)
{
using (SqlConnection conn = new SqlConnection(ConnectionString))
{
conn.Open();
return conn.Query<T>(sql, param);
}
}
internal static int Execute(string sql, object param = null)
{
using (SqlConnection conn = new SqlConnection(ConnectionString))
{
conn.Open();
return conn.Execute(sql, param);
}
}
答案 1 :(得分：14)
大约4年前被问过......但无论如何，也许答案对这里的某人有用：
我在所有项目中都是这样做的。 首先，我创建了一个基类，其中包含一些辅助方法，如下所示：
public class BaseRepository
{
protected T QueryFirstOrDefault<T>(string sql, object parameters = null)
{
using (var connection = CreateConnection())
{
return connection.QueryFirstOrDefault<T>(sql, parameters);
}
}
protected List<T> Query<T>(string sql, object parameters = null)
{
using (var connection = CreateConnection())
{
return connection.Query<T>(sql, parameters).ToList();
}
}
protected int Execute(string sql, object parameters = null)
{
using (var connection = CreateConnection())
{
return connection.Execute(sql, parameters);
}
}
// Other Helpers...
private IDbConnection CreateConnection()
{
var connection = new SqlConnection(...);
// Properly initialize your connection here.
return connection;
}
}
拥有这样的基类我可以轻松地创建真正的存储库，而无需任何样板代码：
public class AccountsRepository : BaseRepository
{
public Account GetById(int id)
{
return QueryFirstOrDefault<Account>("SELECT * FROM Accounts WHERE Id = @Id", new { id });
}
public List<Account> GetAll()
{
return Query<Account>("SELECT * FROM Accounts ORDER BY Name");
}
// Other methods...
}
所以与Dapper，SqlConnection-s和其他数据库访问相关的所有代码都位于一个地方（BaseRepository）。所有真正的存储库都是简洁的单行方法。
我希望它会帮助别人。
答案 2 :(得分：8)
Microsoft.AspNetCore.All ：v2.0.3 | Dapper ：v1.50.2
我不确定我是否正确使用了最佳做法，但我这样做是为了处理多个连接字符串。
Startup.cs
using System.Data;
using System.Data.SqlClient;
namespace DL.SO.Project.Web.UI
{
public class Startup
{
public IConfiguration Configuration { get; private set; }
// ......
public void ConfigureServices(IServiceCollection services)
{
// Read the connection string from appsettings.
string dbConnectionString = this.Configuration.GetConnectionString("dbConnection1");
// Inject IDbConnection, with implementation from SqlConnection class.
services.AddTransient<IDbConnection>((sp) => new SqlConnection(dbConnectionString));
// Register your regular repositories
services.AddScoped<IDiameterRepository, DiameterRepository>();
// ......
}
}
}
DiameterRepository.cs
using Dapper;
using System.Data;
namespace DL.SO.Project.Persistence.Dapper.Repositories
{
public class DiameterRepository : IDiameterRepository
{
private readonly IDbConnection _dbConnection;
public DiameterRepository(IDbConnection dbConnection)
{
_dbConnection = dbConnection;
}
public IEnumerable<Diameter> GetAll()
{
const string sql = @"SELECT * FROM TABLE";
// No need to use using statement. Dapper will automatically
// open, close and dispose the connection for you.
return _dbConnection.Query<Diameter>(sql);
}
// ......
}
}
由于Dapper使用IDbConnection，您需要考虑区分不同数据库连接的方法。
我尝试创建多个界面，＆＃39;继承＆＃39;来自IDbConnection，对应于不同的数据库连接，并在SqlConnection上为Startup注入不同的数据库连接字符串。
失败是因为SqlConnection继承了DbConnection和DbConnection补充，不仅IDbConnection而且Component类。因此，您的自定义界面无法仅使用SqlConnection实现。
我还尝试创建自己的DbConnection类，它接受不同的连接字符串。这太复杂了，因为你必须实现DbConnection类中的所有方法。你失去了SqlConnection的帮助。
Startup期间，我将所有连接字符串值加载到字典中。我还为所有数据库连接名称创建了enum以避免魔术字符串。 IDbConnection，而是创建了IDbConnectionFactory并将其作为Transient注入所有存储库。现在，所有存储库都采用IDbConnectionFactory而不是IDbConnection。DatabaseConnectionName.cs
namespace DL.SO.Project.Domain.Repositories
{
public enum DatabaseConnectionName
{
Connection1,
Connection2
}
}
IDbConnectionFactory.cs
using System.Data;
namespace DL.SO.Project.Domain.Repositories
{
public interface IDbConnectionFactory
{
IDbConnection CreateDbConnection(DatabaseConnectionName connectionName);
}
}
DapperDbConenctionFactory - 我自己的工厂实现
namespace DL.SO.Project.Persistence.Dapper
{
public class DapperDbConnectionFactory : IDbConnectionFactory
{
private readonly IDictionary<DatabaseConnectionName, string> _connectionDict;
public DapperDbConnectionFactory(IDictionary<DatabaseConnectionName, string> connectionDict)
{
_connectionDict = connectionDict;
}
public IDbConnection CreateDbConnection(DatabaseConnectionName connectionName)
{
string connectionString = null;
if (_connectDict.TryGetValue(connectionName, out connectionString))
{
return new SqlConnection(connectionString);
}
throw new ArgumentNullException();
}
}
}
Startup.cs
namespace DL.SO.Project.Web.UI
{
public class Startup
{
// ......
public void ConfigureServices(IServiceCollection services)
{
var connectionDict = new Dictionary<DatabaseConnectionName, string>
{
{ DatabaseConnectionName.Connection1, this.Configuration.GetConnectionString("dbConnection1") },
{ DatabaseConnectionName.Connection2, this.Configuration.GetConnectionString("dbConnection2") }
};
// Inject this dict
services.AddSingleton<IDictionary<DatabaseConnectionName, string>>(connectionDict);
// Inject the factory
services.AddTransient<IDbConnectionFactory, DapperDbConnectionFactory>();
// Register your regular repositories
services.AddScoped<IDiameterRepository, DiameterRepository>();
// ......
}
}
}
DiameterRepository.cs
using Dapper;
using System.Data;
namespace DL.SO.Project.Persistence.Dapper.Repositories
{
// Move the responsibility of picking the right connection string
// into an abstract base class so that I don't have to duplicate
// the right connection selection code in each repository.
public class DiameterRepository : DbConnection1RepositoryBase, IDiameterRepository
{
public DiameterRepository(IDbConnectionFactory dbConnectionFactory)
: base(dbConnectionFactory) { }
public IEnumerable<Diameter> GetAll()
{
const string sql = @"SELECT * FROM TABLE";
// No need to use using statement. Dapper will automatically
// open, close and dispose the connection for you.
return base.DbConnection.Query<Diameter>(sql);
}
// ......
}
}
DbConnection1RepositoryBase.cs
using System.Data;
using DL.SO.Project.Domain.Repositories;
namespace DL.SO.Project.Persistence.Dapper
{
public abstract class DbConnection1RepositoryBase
{
public IDbConnection DbConnection { get; private set; }
public DbConnection1RepositoryBase(IDbConnectionFactory dbConnectionFactory)
{
// Now it's the time to pick the right connection string!
// Enum is used. No magic string!
this.DbConnection = dbConnectionFactory.CreateDbConnection(DatabaseConnectionName.Connection1);
}
}
}
然后，对于需要与其他连接通信的其他存储库，您可以为它们创建不同的存储库基类。
using System.Data;
using DL.SO.Project.Domain.Repositories;
namespace DL.SO.Project.Persistence.Dapper
{
public abstract class DbConnection2RepositoryBase
{
public IDbConnection DbConnection { get; private set; }
public DbConnection2RepositoryBase(IDbConnectionFactory dbConnectionFactory)
{
this.DbConnection = dbConnectionFactory.CreateDbConnection(DatabaseConnectionName.Connection2);
}
}
}
using Dapper;
using System.Data;
namespace DL.SO.Project.Persistence.Dapper.Repositories
{
public class ParameterRepository : DbConnection2RepositoryBase, IParameterRepository
{
public ParameterRepository (IDbConnectionFactory dbConnectionFactory)
: base(dbConnectionFactory) { }
public IEnumerable<Parameter> GetAll()
{
const string sql = @"SELECT * FROM TABLE";
return base.DbConnection.Query<Parameter>(sql);
}
// ......
}
}
希望所有这些帮助。
答案 3 :(得分：6)
最佳实践是一个真正的负载术语。我喜欢像Dapper.Rainbow推广的DbDataContext样式容器。它允许您结合CommandTimeout，交易和其他帮助。
例如：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using Dapper;
// to have a play, install Dapper.Rainbow from nuget
namespace TestDapper
{
class Program
{
// no decorations, base class, attributes, etc
class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public DateTime? LastPurchase { get; set; }
}
// container with all the tables
class MyDatabase : Database<MyDatabase>
{
public Table<Product> Products { get; set; }
}
static void Main(string[] args)
{
var cnn = new SqlConnection("Data Source=.;Initial Catalog=tempdb;Integrated Security=True");
cnn.Open();
var db = MyDatabase.Init(cnn, commandTimeout: 2);
try
{
db.Execute("waitfor delay '00:00:03'");
}
catch (Exception)
{
Console.WriteLine("yeah ... it timed out");
}
db.Execute("if object_id('Products') is not null drop table Products");
db.Execute(@"create table Products (
Id int identity(1,1) primary key,
Name varchar(20),
Description varchar(max),
LastPurchase datetime)");
int? productId = db.Products.Insert(new {Name="Hello", Description="Nothing" });
var product = db.Products.Get((int)productId);
product.Description = "untracked change";
// snapshotter tracks which fields change on the object
var s = Snapshotter.Start(product);
product.LastPurchase = DateTime.UtcNow;
product.Name += " World";
// run: update Products set LastPurchase = @utcNow, Name = @name where Id = @id
// note, this does not touch untracked columns
db.Products.Update(product.Id, s.Diff());
// reload
product = db.Products.Get(product.Id);
Console.WriteLine("id: {0} name: {1} desc: {2} last {3}", product.Id, product.Name, product.Description, product.LastPurchase);
// id: 1 name: Hello World desc: Nothing last 12/01/2012 5:49:34 AM
Console.WriteLine("deleted: {0}", db.Products.Delete(product.Id));
// deleted: True
Console.ReadKey();
}
}
}
答案 4 :(得分：6)
我这样做：
internal class Repository : IRepository {
private readonly Func<IDbConnection> _connectionFactory;
public Repository(Func<IDbConnection> connectionFactory)
{
_connectionFactory = connectionFactory;
}
public IWidget Get(string key) {
using(var conn = _connectionFactory())
{
return conn.Query<Widget>(
"select * from widgets with(nolock) where widgetkey=@WidgetKey", new { WidgetKey=key });
}
}
}
然后，无论我在哪里连接我的依赖项（例如：Global.asax.cs或Startup.cs），我都会这样做：
var connectionFactory = new Func<IDbConnection>(() => {
var conn = new SqlConnection(
ConfigurationManager.ConnectionStrings["connectionString-name"];
conn.Open();
return conn;
});
答案 5 :(得分：4)
试试这个：
public class ConnectionProvider
{
DbConnection conn;
string connectionString;
DbProviderFactory factory;
// Constructor that retrieves the connectionString from the config file
public ConnectionProvider()
{
this.connectionString = ConfigurationManager.ConnectionStrings[0].ConnectionString.ToString();
factory = DbProviderFactories.GetFactory(ConfigurationManager.ConnectionStrings[0].ProviderName.ToString());
}
// Constructor that accepts the connectionString and Database ProviderName i.e SQL or Oracle
public ConnectionProvider(string connectionString, string connectionProviderName)
{
this.connectionString = connectionString;
factory = DbProviderFactories.GetFactory(connectionProviderName);
}
// Only inherited classes can call this.
public DbConnection GetOpenConnection()
{
conn = factory.CreateConnection();
conn.ConnectionString = this.connectionString;
conn.Open();
return conn;
}
}
答案 6 :(得分：2)
每个人似乎都过早地打开了他们的联系？我有同样的问题，在这里挖掘了来源 - https://github.com/StackExchange/dapper-dot-net/blob/master/Dapper/SqlMapper.cs
您会发现与数据库的每次交互都会检查连接是否已关闭，并根据需要打开它。因此，我们只使用上面的语句而不使用conn.open（）。这样，连接打开时尽可能接近交互。如果您注意到，它也会立即关闭连接。这也比处理过程中自动关闭更快。
上面的回购中的众多例子之一：
private static int ExecuteCommand(IDbConnection cnn, ref CommandDefinition command, Action<IDbCommand, object> paramReader)
{
IDbCommand cmd = null;
bool wasClosed = cnn.State == ConnectionState.Closed;
try
{
cmd = command.SetupCommand(cnn, paramReader);
if (wasClosed) cnn.Open();
int result = cmd.ExecuteNonQuery();
command.OnCompleted();
return result;
}
finally
{
if (wasClosed) cnn.Close();
cmd?.Dispose();
}
}
以下是我们如何使用Dapper的Wrapper称为DapperWrapper的一个小例子。这允许我们包装所有Dapper和Simple Crud方法来管理连接，提供安全性，日志记录等。
public class DapperWrapper : IDapperWrapper
{
public IEnumerable<T> Query<T>(string query, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null)
{
using (var conn = Db.NewConnection())
{
var results = conn.Query<T>(query, param, transaction, buffered, commandTimeout, commandType);
// Do whatever you want with the results here
// Such as Security, Logging, Etc.
return results;
}
}
}
答案 7 :(得分：0)
嗨@donaldhughes我也是新手，我用它来做： 1 - 创建一个类来获取我的连接字符串 2 - 在使用
中调用连接字符串类查找
<强> DapperConnection.cs
public class DapperConnection
{
public IDbConnection DapperCon {
get
{
return new SqlConnection(ConfigurationManager.ConnectionStrings["Default"].ToString());
}
}
}
<强> DapperRepository.cs
public class DapperRepository : DapperConnection
{
public IEnumerable<TBMobileDetails> ListAllMobile()
{
using (IDbConnection con = DapperCon )
{
con.Open();
string query = "select * from Table";
return con.Query<TableEntity>(query);
}
}
}
它运作正常。
答案 8 :(得分：0)
我用helper类包装连接：
public class ConnectionFactory
{
private readonly string _connectionName;
public ConnectionFactory(string connectionName)
{
_connectionName = connectionName;
}
public IDbConnection NewConnection() => new SqlConnection(_connectionName);
#region Connection Scopes
public TResult Scope<TResult>(Func<IDbConnection, TResult> func)
{
using (var connection = NewConnection())
{
connection.Open();
return func(connection);
}
}
public async Task<TResult> ScopeAsync<TResult>(Func<IDbConnection, Task<TResult>> funcAsync)
{
using (var connection = NewConnection())
{
connection.Open();
return await funcAsync(connection);
}
}
public void Scope(Action<IDbConnection> func)
{
using (var connection = NewConnection())
{
connection.Open();
func(connection);
}
}
public async Task ScopeAsync<TResult>(Func<IDbConnection, Task> funcAsync)
{
using (var connection = NewConnection())
{
connection.Open();
await funcAsync(connection);
}
}
#endregion Connection Scopes
}
用法示例：
public class PostsService
{
protected IConnectionFactory Connection;
// Initialization here ..
public async Task TestPosts_Async()
{
// Normal way..
var posts = Connection.Scope(cnn =>
{
var state = PostState.Active;
return cnn.Query<Post>("SELECT * FROM [Posts] WHERE [State] = @state;", new { state });
});
// Async way..
posts = await Connection.ScopeAsync(cnn =>
{
var state = PostState.Active;
return cnn.QueryAsync<Post>("SELECT * FROM [Posts] WHERE [State] = @state;", new { state });
});
}
}
所以我不必每次都明确打开连接。 此外，为方便将来的重构，您可以这样使用它：
var posts = Connection.Scope(cnn =>
{
var state = PostState.Active;
return cnn.Query<Post>($"SELECT * FROM [{TableName<Post>()}] WHERE [{nameof(Post.State)}] = @{nameof(state)};", new { state });
});
TableName<T>()中可以找到Total的内容。