I have an architecture where multiple repository classes implement different queries and commands that are run against the database. I would like to separate the concern of "connecting to the database" + "running queries" and "providing a query to run" + "treating the result". I've written a Connection class that is then passed as a constructor argument to the repositories like such:
public class PostgreSqlConnection
{
private string connectionString;
public PostgreSqlConnection(string connectionString)
{
this.connectionString = connectionString;
}
public async Task<NpgsqlDataReader> ExecuteQueryCommand(NpgsqlCommand command)
{
using NpgsqlConnection connection = new NpgsqlConnection(this.connectionString);
await connection.OpenAsync();
command.Connection = connection;
command.Prepare();
return await command.ExecuteReaderAsync();
}
public async Task ExecuteNonQueryCommand(NpgsqlCommand command)
{
using NpgsqlConnection connection = new NpgsqlConnection(this.connectionString);
await connection.OpenAsync();
command.Connection = connection;
command.Prepare();
await command.ExecuteNonQueryAsync();
}
}
The instantiation would look something like this:
PostgreSqlConnection connection = new PostgreSqlConnection("...connection string");
IRepositoryA repA = new PostgreSqlRepositoryA(connection);
IRepositoryB repB = new PostgreSqlRepositoryB(connection);
Code duplication aside, this doesn't work since in the query case, the connection would be disposed of at the end of the ExecuteQueryCommand method and the reader would stop working.
Removing the using statement would fix this but from what I gather that is not good practice. Writing a Dispose / Disconnect method that I could call in the repositories would be something that would also work but it's not the repository's job to dispose of the connection.
How could I go about keeping the concerns separated and disposing of the items properly?
I think what here can help is a Unit of Work pattern. Basically, with UnitOfWork class you handle the connection, repository instances and transactions if needed (in case you are saving data to DB). You also have a flexibility to open a connection/transaction and then execute multiple commands across many repositories and in the end you either commit or rollback the transaction, or in case of pure reading you just close the connection using IDisposable pattern.
UnitOfWork class will handle the connection part, your BaseRepository (abstract class) will have your generic execute methods and it will handle the execution of query/command. The concrete repositories (A and B in your case) will inherit from BaseRepository, just prepare the commands/queries and call the Execute methods from a BaseRepository. Their responsibility is basically to prepare the query/command and to handle the result from Execute methods.
Please review the code because I don't have Postgres database and I can't test it 100%. I hope this is enough for you to give you a direction and the main idea behind the approach.
Here is the idea:
Implement UnitOfWork where you manange the connection, transaction if needed and repository instances.
public class UnitOfWork : IDisposable
{
private PostgreSqlRepositoryA _postgreSqlRepositoryA;
private PostgreSqlRepositoryB _postgreSqlRepositoryB;
private NpgsqlConnection _sqlConnection;
private NpgsqlTransaction _sqlTransaction;
private bool _disposed;
public UnitOfWork(string connectionString, bool withTransaction)
{
_sqlConnection = new NpgsqlConnection(connectionString);
_sqlConnection.Open();
if (withTransaction)
_sqlTransaction = _sqlConnection.BeginTransaction();
}
public PostgreSqlRepositoryA PostgreSqlRepositoryA
{
get
{
if(_postgreSqlRepositoryA == null)
{
_postgreSqlRepositoryA = new PostgreSqlRepositoryA(_sqlConnection);
}
return _postgreSqlRepositoryA;
}
}
public PostgreSqlRepositoryB PostgreSqlRepositoryB
{
get
{
if (_postgreSqlRepositoryB == null)
{
_postgreSqlRepositoryB = new PostgreSqlRepositoryB(_sqlConnection);
}
return _postgreSqlRepositoryB;
}
}
public void Commit()
{
// hanlde using try-catch
if(_sqlTransaction != null)
{
_sqlTransaction.Commit();
}
}
public void Rollback()
{
if (_sqlTransaction != null)
{
_sqlTransaction.Rollback();
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!this._disposed)
{
if (_sqlTransaction != null)
{
_sqlTransaction.Rollback(); // or throw an Exception for an opened transaction
}
if (_sqlConnection != null)
{
_sqlConnection.Close();
_sqlConnection.Dispose();
}
this._disposed = true;
}
}
}
Then what you need is a BaseRepository which will hold your "generic" methods for query/command execution:
public abstract class BaseRepository
{
protected NpgsqlConnection _sqlConnection;
public BaseRepository(NpgsqlConnection sqlConnection)
{
this._sqlConnection = sqlConnection;
}
public async Task<NpgsqlDataReader> ExecuteQueryCommand(NpgsqlCommand command)
{
command.Connection = _sqlConnection;
command.Prepare();
return await command.ExecuteReaderAsync();
}
public async Task ExecuteNonQueryCommand(NpgsqlCommand command)
{
command.Connection = _sqlConnection;
command.Prepare();
await command.ExecuteNonQueryAsync();
}
}
Your concrete repository implementation will look like this (I didn't bother with handling the reader, you can add that part):
public class PostgreSqlRepositoryB : BaseRepository
{
public PostgreSqlRepositoryB(NpgsqlConnection sqlConnection)
: base(sqlConnection)
{}
public async Task<int> GetCountB()
{
using (var sqlCommand = new NpgsqlCommand())
{
sqlCommand.CommandText = "select count(1) from TableB";
var reader = await ExecuteQueryCommand(sqlCommand);
// TODO: handle reader
}
}
}
And the in the end you will use it from your service or client method like this (if your are just reading from DB then set withTransaction to false, you don't need a transaction in that case):
using(var uow = new UnitOfWork("place_your_conn_string", withTransaction: true))
{
var countB = await uow.PostgreSqlRepositoryB.GetCountB();
uow.PostgreSqlRepositoryB.SaveSomethingToA("123456");
uow.Commit();
}
This is my code so far:
public class ServerUtility
{
public static int LogError(string source, string detail)
{
int iresult = -99;
try
{
BaseRepository repo = new BaseRepository();
using (SqlConnection con = new SqlConnection(repo.connectionString))
{
con.Open();
using (SqlCommand cmd = new SqlCommand($"INSERT INTO [dbo].[LogError]([source],[detail],[date])VALUES('{source.Replace("'", "''")}','{detail.Replace("'", "''")}',GETDATE());SELECT ##IDENTITY", con))
{
string getValue = cmd.ExecuteScalar().ToString();
iresult = Convert.ToInt32(getValue);
} // command disposed here
} //connection closed and disposed here
}
catch (Exception ex) { throw ex; }
return iresult;
}
}
My question is on GetInstance method :
BaseRepository repo = new BaseRepository();
using (SqlConnection con = new SqlConnection(repo.connectionString))
I am always set it as new object, on my static function, just for get constant value from AppSetting.
What actually happened if I implement this code to my project?
How about the performance?
Is it cause performance issue?
Thanks
Like #gtosto mentioned, you're not implementing singletons correctly.
It should be:
public static SenderBackupProvider GetInstance()
{
if (oInstance == null)
{
oInstance = new SenderBackupProvider(CommFunction.GetLogNumber(CommonConst.APPID));
}
return oInstance;
}
Check out Implementing the Singleton Pattern in C#.
EDIT:
Since OP doesn't believe that the oInstance variable should be null on first time run, here's a screenshot.
Upon a closer look at your code, you are using a web application. The life cycle of static variables differ from one platform to the other. You might need to do an app domain restart in IIS. See more information in Lifetime of ASP.NET Static Variable.
I am trying to read through a stored SQLiteDataReader object. In theory, it "should" work because the object is stored in a variable before it is referenced (and doesn't hit an error until the reference line is reached), but maybe I have the wrong idea.
I'm trying to keep my application in a neatly layered architecture. So, each database table having its own C# class with its own methods for select, insert, update, and delete; only the data layer knows how to communicate with the database, etc.
I was running into connection issues earlier when I tried to make one static SQLiteConnection object that all the data layer classes could reference (so as to keep it open and minimize overhead, if any). So I'm trying to go with the using block to make sure the connection is properly disposed each time I need to access the database, and hoping that this won't cause performance issues.
So basically, here is the method in my DatabaseConnection class that handles basic query execution:
public SQLiteDataReader ExecuteQuery(string sql)
{
SQLiteDataReader rdr = null;
using(SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
conn.Open();
SQLiteCommand cmd = conn.CreateCommand();
cmd.CommandText = sql;
rdr = cmd.ExecuteReader();
}
return rdr;
}
And here is the code that calls that method. I'll use an object/record of the Associate table as an example.
public class Associate
{
public int RowId { get; private set; }
public int Id { get; set; }
public string Name { get; set; }
private string password;
public string Password
{
get
{
return password;
}
set
{
password = Hash(value); // external password hashing method
}
}
public Associate() { } // default constructor with default values
public Associate(int id)
{
this.Id = id;
Select();
}
// select, insert, update, delete methods
private void Select() { ... }
// these are non-queries and return true/false based on success
public bool Insert() { ... }
public bool Update() { ... }
public bool Delete() { ... }
/* Method that causes the error */
public static Associate[] GetAll()
{
DatabaseConnection con = new DatabaseConnection();
SQLiteDataReader rdr = con.ExecuteQuery("SELECT id FROM Associate");
List<Associate> list = new List<Associate>();
if (rdr != null)
{
while (rdr.Read()) /* this line throws the exception */
{
int next = rdr.GetInt32(0);
list.Add(new Associate(next));
}
}
return list.ToArray();
}
}
The idea here is that using the rdr object, I can access the column names directly so that if the database ever changes, I won't have to rewrite a bunch of code to adjust for the column indices (rdr["id"], rdr["name"], etc.)
So what I don't understand is why rdr in the calling method is having "object disposed" issues because it's stored in a variable before I reference it. I know the connection is disposed at the end of the called method, but since the returned result is stored, shouldn't it technically be able to "survive" outside the using block?
It is the connection that got disposed. The data reader can only read data while the connection still exists.
public SQLiteDataReader ExecuteQuery(string sql)
{
SQLiteDataReader rdr = null;
using(SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
conn.Open();
SQLiteCommand cmd = conn.CreateCommand();
cmd.CommandText = sql;
rdr = cmd.ExecuteReader();
}
// *** Connection gone at this stage ***
return rdr;
}
Your options are to either return a DataTable, e.g.
public DataTable ExecuteQuery(string sql)
{
SQLiteDataReader rdr = null;
using(SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
conn.Open();
SQLiteCommand cmd = conn.CreateCommand();
cmd.CommandText = sql;
rdr = cmd.ExecuteReader();
var dataTable = new DataTable();
dataTable.Load(rdr);
return dataTable;
}
}
otherwise, you could keep the connection alive inside the DatabaseConnection class:
class DatabaseConnection : IDisposable
{
private readonly IDbConnection _conn;
public DatabaseConnection()
{
_conn = new SQLiteConnection(ConnectionString);
}
public void Dispose()
{
_conn.Dispose();
}
public SQLDataReader ExecuteQuery(string sql)
{
...
}
}
// sample usage
using (var conn = new DatabaseConnection())
{
using (var reader = conn.ExecuteQuery("SELECT ...")
{
// do your work in here
}
}
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
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.
I injected the dictionary as Singleton.
Instead of injecting IDbConnection, I created IDbConnectionFactory and injected that as Transient for all repositories. Now all repositories take IDbConnectionFactory instead of IDbConnection.
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.
In C# I am able to create a class like this:
static class clsDBUtils
{
public static SQLiteCommand cmd;
public static SQLiteConnection conn;
public static String databaseFilePath;
public static bool getConnection()
{
}
}
Then anywhere in my namespace can use without initialization this way:
clsDBUtils.getConnection();
How can this be rewritten for Java?
I don't want to use:
clsDBUtils sqlutil= new clsDBUtils();
Basically the same way, just make a (normal) final class with a private contructor (prevents being able to do new) and add static members only.
public final class clsDBUtils {
public static SQLiteCommand cmd;
public static SQLiteConnection conn;
public static String databaseFilePath;
public static bool getConnection() {
}
private clsDBUtils() {}
}
Apart from the particular question/problem, it is bad practice to declare expensive and external resources like Connection, Statement and ResultSet as an instance variable, let alone as a static variable. Those resources doesn't have an endless lifetime and your application may break when the DB decides to timeout the connection because it hasn't been released back to the DB after use.
I can't imagine that it's done differently in C# (it would have been a bug in the application as well), but the normal JDBC idiom is that you acquire and close it in the shortest possible scope, thus already inside the very same method block. E.g.
public Entity find(Long id) throws SQLException {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
Entity entity = null;
try {
connection = database.getConnection();
statement = connection.prepareStatement(SQL_FIND);
statement.setLong(1, id);
resultSet = statement.executeQuery();
if (resultSet.next()) {
entity = new Entity();
entity.setProperty(resultSet.getObject("columnname"));
// etc..
}
} finally {
// Always free resources in reversed order.
if (resultSet != null) try { resultSet.close(); } catch (SQLException logOrIgnore) {}
if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
if (connection != null) try { connection.close(); } catch (SQLException logOrIgnore) {}
}
return entity;
}
The database.getConnection() can however technically perfectly be made static like this:
public final class Database {
static {
try {
Class.forName("com.example.jdbc.Driver");
} catch (ClassNotFoundException e) {
throw new ExceptionInInitializerError(e);
}
}
private Database() {
// No need to instantiate this class.
}
public static Connection getConnection() {
DriverManager.getConnection("jdbc:example://localhost/dbname", "user", "pass");
}
}
so that you can use it as
connection = Database.getConnection();
(which you still really need to close in the finally block after use!)
However, this makes the connection source also really static. You cannot take benefit of polymorphism and/or inheritance anymore to switch between connection sources, such as a connection pool (to get better performance). To get more ideas/insights you may find this article useful
The code for it is almost exactly the same (same concept, slightly different syntax)
public class ClsDBUtils
{
public static SQLiteCommand cmd;
public static SQLiteConnection conn;
public static String databaseFilePath;
public static boolean getConnection()
{
}
}
// somewhere else
ClsDBUtils.getConnection();
Just declare a public class and use the 'static' modifier on your methods and fields. If you do not want it to be instantiated, use 'public final class '. Alternatively, you can use a singleton class.
You want to implement the Singleton pattern: http://en.wikipedia.org/wiki/Singleton_pattern
public class clsDBUtils {
private static final clsDBUtils INSTANCE = new clsDBUtils();
// Private constructor prevents instantiation from other classes
private clsDBUtils() {}
public static clsDBUtils getInstance() {
return INSTANCE;
}
public SQLiteCommand cmd;
public SQLiteConnection conn;
public String databaseFilePath;
public bool getConnection()
{
}
}
You can then use the following syntax on your class:
clsDBUtils.getInstance().getConnection();