How do I handle Database Connections with Dapper in .NET?

I've been playing with Dapper, but I'm not sure of the best way to handle the database connection.

Most examples show the connection object being created in the example class, or even in each method. But it feels wrong to me to reference a connection string in every clss, even if it's pulling from the web.config.

My experience has been with using a DbDataContext or DbContext with Linq to SQL or Entity Framework, so this is new to me.

How do I structure my web apps when using Dapper as my Data Access strategy?

Update: clarification from MarredCheese's comment:

> "No need to use a using statement. Dapper will automatically open, > close, and dispose of the connection for you." That's not correct. > Dapper will automatically open closed connections, and it will > automatically close connections that it auto-opened, but it will not > automatically dispose of connections. Marc Gravell and Eric Lippert > both advocate using using with Dapper here.

Microsoft.AspNetCore.All: v2.0.3 | Dapper: v1.50.2

I am not sure if I am using the best practices correctly or not, but I am doing it this way, in order to handle multiple connection strings.

It's easy if you have only 1 connection string

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);
        }

        // ......
    }
}

Problems if you have more than 1 connection string

Since Dapper utilizes IDbConnection, you need to think of a way to differentiate different database connections.

I tried to create multiple interfaces, 'inherited' from IDbConnection, corresponding to different database connections, and inject SqlConnection with different database connection strings on Startup.

That failed because SqlConnection inherits from DbConnection, and DbConnection inplements not only IDbConnection but also Component class. So your custom interfaces won't be able to use just the SqlConnection implenentation.

I also tried to create my own DbConnection class that takes different connection string. That's too complicated because you have to implement all the methods from DbConnection class. You lost the help from SqlConnection.

What I end up doing

1. During Startup, I loaded all connection string values into a dictionary. I also created an enum for all the database connection names to avoid magic strings.
2. I injected the dictionary as Singleton.
3. Instead of injecting IDbConnection, I created IDbConnectionFactory and injected that as Transient for all repositories. Now all repositories take IDbConnectionFactory instead of IDbConnection.
4. When to pick the right connection? In the constructor of all repositories! To make things clean, I created repository base classes and have the repositories inherit from the base classes. The right connection string selection can happen in the base classes.

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 - my own factory implementation

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);
        }
    }
}

Then for other repositories that need to talk to the other connections, you can create a different repository base class for them.

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);
        }

        // ......
    }
}

Hope all these help.

It was asked about 4 years ago... but anyway, maybe the answer will be useful to someone here:

I do it like this in all the projects. First, I create a base class which contains a few helper methods like this:

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;
    }
}

And having such a base class I can easily create real repositories without any boilerplate code:

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...
}

So all the code related to Dapper, SqlConnection-s and other database access stuff is located in one place (BaseRepository). All real repositories are clean and simple 1-line methods.

I hope it will help someone.

I created extension methods with a property that retrieves the connection string from configuration. This lets the callers not have to know anything about the connection, whether it's open or closed, etc. This method does limit you a bit since you're hiding some of the Dapper functionality, but in our fairly simple app it's worked fine for us, and if we needed more functionality from Dapper we could always add a new extension method that exposes it.

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);
        }
    }

I do it like this:

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 });
        }
    }
}

Then, wherever I wire-up my dependencies (ex: Global.asax.cs or Startup.cs), I do something like:

var connectionFactory = new Func<IDbConnection>(() => {
    var conn = new SqlConnection(
        ConfigurationManager.ConnectionStrings["connectionString-name"];
    conn.Open();
    return conn;
});

Best practice is a real loaded term. I like a DbDataContext style container like Dapper.Rainbow promotes. It allows you to couple the CommandTimeout, transaction and other helpers.

For example:

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();
        }
    }
}

Try this:

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;
        }

    }

Everyone appears to be opening their connections entirely too early? I had this same question, and after digging through the Source here - https://github.com/StackExchange/dapper-dot-net/blob/master/Dapper/SqlMapper.cs

You will find that every interaction with the database checks the connection to see if it is closed, and opens it as necessary. Due to this, we simply utilize using statements like above without the conn.open(). This way the connection is opened as close to the interaction as possible. If you notice, it also immediately closes the connection. This will also be quicker than it closing automatically during disposal.

One of the many examples of this from the repo above:

    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();
        }
    }

Below is a small example of how we use a Wrapper for Dapper called the DapperWrapper. This allows us to wrap all of the Dapper and Simple Crud methods to manage connections, provide security, logging, etc.

  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;
	  }
	}
  }

I wrap connection with the helper class:

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
}

Examples of usage:

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 });
        });
    }
}

So I don't have to explicitly open the connection every time. Additionally, you can use it this way for the convenience' sake of the future refactoring:

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 });
});

What is TableName<T>() can be found in this answer.

Hi @donaldhughes I'm new on it too, and I use to do this: 1 - Create a class to get my Connection String 2 - Call the connection string class in a Using

Look:

DapperConnection.cs

public class DapperConnection
{

    public IDbConnection DapperCon {
        get
        {
            return new SqlConnection(ConfigurationManager.ConnectionStrings["Default"].ToString());
            
        }
    }
}

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);
            }
        }
     }

And it works fine.