I have the following code which I use frequently with Android and iOS when creating apps. Simply, it creates a lock when inserting, creating or updating a table.
public class SQL
{
readonly object dbLock = new object();
const string DBClauseSyncOff = "PRAGMA SYNCHRONOUS=OFF;";
const string DBClauseVacuum = "VACUUM;";
#region Setup
public bool SetupDB()
{
lock (dbLock)
As soon as the WinPhone 8.1 app hits this lock line, an exception is thrown. As this is part of a Xam.Forms application, I call this into existence using the following
public App()
{
App.Self = this;
var netLanguage = DependencyService.Get<ILocalise>().GetCurrent();
LangResources.Culture = new CultureInfo(netLanguage);
ConnectionString = DependencyService.Get<ISQLite>().GetConnectionString();
App.Self.SQLitePlatform = DependencyService.Get<ISQLite>().GetPlatform();
DBManager = new SQL();
DBManager.SetupDB();
Nothing is being called asynchronously with the two dependency services returning as their names suggest the connection and platform in use.
The calls look like this
public string GetConnectionString()
{
var documents = ApplicationData.Current.LocalFolder.Path;
var pConnectionString = System.IO.Path.Combine(documents, "preferences.db");
var connectionString = string.Format("{0}; New=true; Version=3;PRAGMA locking_mode=NORMAL; PRAGMA journal_mode=WAL; PRAGMA cache_size=20000; PRAGMA page_size=32768; PRAGMA synchronous=off", pConnectionString);
return connectionString;
}
public ISQLitePlatform GetPlatform()
{
return new SQLite.Net.Platform.WinRT.SQLitePlatformWinRT();
}
If I comment out the SetupDB line, the app runs as I would expect. If it is left in, the app crashes with the error that it cannot create the initial display.
Is there something I need to be doing (or not doing) in order for the DB code to work on all platforms and not just Android and iOS?
I have a class that gets tables from Sql Server. the class is static, but the variables are not. I want to know if it is OK in Asp net, because I had read not to use static at database in Asp net.
My Class: (There are more functions in the class, I put here one for example)
public static class DataBase
{
public static bool TableChange(string sqlCreate)
{
using (SqlConnection connection = new SqlConnection(Global.ConnectionString))
{
using (var cmd = new SqlCommand(sqlCreate, connection))
{
try
{
connection.Open();
cmd.ExecuteNonQuery();
}
catch (Exception ex)
{
Log.WriteLog(ex.Message + "\n" + sqlCreate, ex, HttpContext.Current.Request);
return false;
}
}
}
return true;
}
}
Thanks in advance
What you have read is most probably something to do with this approach:
public static EntityContext Database = new EntityContext();
// or
public static SqlConnection Database = new SqlConnection("...");
Here you store the database connection in a static variable and thus all parallel requests would want to use the same connection which is a very bad approach if it even works at all (it will probably work sort of fine until the page is under load).
You do not have this problem, because in your case only the methods are static, not the variables. Your code follows the recommended path - open connection (retrieve it from the pool), execute query, close the connection (return it to the pool).
i working with entity famework i need to transfer that code
RESTORE DATABASE [showing8-5-2013] FROM DISK = N'C:\Program Files (x86)\Microsoft SQL Server\MSSQL10_50.SQLEXPRESS\MSSQL\Backup\Company.bak' WITH FILE = 1, NOUNLOAD, REPLACE, STATS = 10
to code Entity frame work
any help thanks
EF is a DB neutral provider concept. Such commands are by their nature DB specific. EF exposes a way to execute an SQL command:
MyContext.Database.ExecuteSqlCommand();
But you may as well just do it directly.
Pass your SQL command into a custom routine eg:
private static bool ExecuteSqlStatement(string connectionString, string statement) {
int rowsAffected;
using (var sqlConnection = new SqlConnection(connectionString)) {
using (var sqlCommand = new SqlCommand(statement, sqlConnection)) {
try {
sqlConnection.Open();
rowsAffected = sqlCommand.ExecuteNonQuery();
}
catch (Exception ex) {
// your handler or re-throw....
return false;
}
}
}
return rowsAffected == -1;
// see http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.executenonquery.aspx
}
Note: I DON't want to write custom membership provider.
I want to write my own Provider class so I can define it in web.config and access it like Membership class.
Here is a sample of my class (it has many other static methods):
public static class MySqlHelper
{
private static string constring = ConfigurationManager.ConnectionStrings["MyConnString"].ConnectionString;
public static int ExecuteNonQuery(string mysqlquery)
{
SqlConnection conn = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(mysqlquery, conn);
int result;
try
{
conn.Open();
result= cmd.ExecuteNonQuery();
}
finally
{
conn.Close();
}
return result;
}
}
Usage: MySqlHelper.ExecuteNonQuery("select * from customers");
Now as you see I have hard-coded the name of connectionstring i.e. "MyConnString". I am planning to make it dynamic.
So I was wondering if I can make it like static built-in Membership class, where I can define the connectionStringName in web.config. This way the class can be made re-usable without always naming my connectionstring in web.config to "MyConnString".
1: I DON'T want to pass connectionstring in every static method as a parameter.
2: I must be able to access the methods similar to Membership.CreateUser i.e. static.
I am looking over the web in parallel but any inputs/guidance will help.
Edited: I have updated my code sample, to clear some confusion about issues using static class. Here is a new question I posted to clarify that. Sorry about confusion.
the only thing i can think of that meets the qualifications you laid out is to use dependency injection, a static constructor, and inject in an something like an IConnectionStringProvider. this seems like about the most convoluted thing i can think of, so you might like it. :)
edit
after reading your comment, it seems like you just want to be able to reference any connection string, but only one connection string per application. i'd say just add an element to appSettings named MySqlProviderConnection with the value being the name of the connection string you want to use.
then in your helper, check for the existence of the appsetting, get its value, and pass it in to your ConfigurationManager.ConnectionStrings call. that way your provider could use any connection you want, without changing any code.
I typically discourage sharing one SqlConnection instance across several requests. Even if you enable MARS, you can run into performance issues. I think when your connection receives a non-read command, the connection buffer will pause all current reads until the write finishes. The only thing you're really saving is the time it takes to establish a connection.
SqlConnections are pooled so you can configure the provider to have a min / max number of instances available to soliciting clients. Keep in mind this is also controlled by whatever database you're connecting to; assuming you're connecting to a SQL Server instance, SQL Server has its own maximum connections allowed setting.
Instead of allowing clients to determine when to open/close a shared SqlConnection instance, I suggest having your public members take in either a command string or command parameters. Then, similar to what your sample has suggested, open a connection from the pool and execute the command.
public IEnumerable<SqlResults> ExecuteStoredProcedure(string procedure, params SqlParameter[] parameters) {
using(SqlConnection connection = new SqlConnection(MyConnectionStringProperty)) {
try {
connection.Open();
using(SqlCommand command = new SqlCommand(procedure, connection)) {
command.CommandType = CommandType.StoredProcedure;
if(parameters != null) {
command.Parameters.AddRange(parameters);
}
// yield return to handle whatever results from proc execution
// can also consider expanding to support reader.NextResult()
using(SqlDataReader reader = command.ExecuteReader()) {
yield return new SqlResults {
Reader = reader;
};
}
}
}
finally {
if(connection.State != ConnectionState.Closed) {
connection.Close();
}
}
}
}
The sample code above is just that - a sample of a concept I use at work. The sample does now have maximized error handling but is very flexible in how results are returned and handled. The SqlResults class simply contains a SqlDataReader property and can be expanded to include errors.
As far as making any of this static, it should be fine as long as you enable a way to make a singleton instance of the provider class and continue to not have any mutable properties be shared (potentially across various requests/threads). You may want to consider some sort of IoC or Dependency Injection approach for providing the connection string given your request.
EDIT
Yield allows the caller to use the returned object before the execution context returns to the method yielding the return for continued execution. So in the sample above, a caller can do something like this:
// Since it's an IEnumerable we can handle multiple result sets
foreach(SqlResults results in MySqlHelper.ExecuteStoredProcedure(myProcedureName, new SqlParameter("myParamName", myParamValue)) {
// handle results
}
without the connection closing while we handle the results. If you notice in the sample, we have using statements for our SqlClient objects. This approach allows result set handling to be decoupled from MySqlHelper as the provider class will take care of the would-be-duplicate SQL provision code, delegate result handling to the caller, then continue with what it has to do (i.e. close the connection).
As for IoC/DI, I personally use Castle Windsor. You can inject dependency objects as properties or construction parameters. Registering an Inversion of Control container as your dependency resource manager will allow you to (among other things) return the same object when a type of resource is requested. Basically, for every caller class that needs to use MySqlHelper, you can inject the same instance when the caller class is instantiated or when the caller class references its public MySqlHelper property. I, personally, prefer constructor injection whenever possible. Also, when I say inject, I mean you don't have to worry about setting the property value as your IoC/DI does it for you (if configured properly). See here for a more in depth explanation.
As another note, the IoC/DI approach would really only come into play if your class is non-static such that each application can have its own singleton instance. If MySqlHelper is static, then you could only support one connection string unless you pass it in, which in your original question, you'd prefer not to do so. IoC/DI will allow you to use your MySqlHelper property member as if it were static though since the registered container would ensure that the property has a proper instance.
Here is the complete code of a SqlHelper that I'd used on some small projects.
But carefull with static for this kind of class. If you will use it for Web project, remember that the connection will be shared at the same instance for all users, which can cause bad problems...
using System.Data;
using System.Data.SqlClient;
using System.Web.Configuration;
public class SqlHelper
{
private SqlConnection connection;
public SqlHelper()
{
connection = new SqlConnection();
}
public void OpenConnection()
{
// Updated code getting the ConnectionString without hard naming it.
// Yes, if you have more than 1 you'll have problems... But, how many times it happens?
if (WebConfigurationManager.ConnectionStrings.Length == 0)
throw new ArgumentNullException("You need to configure the ConnectionString on your Web.config.");
else
{
connection.ConnectionString = WebConfigurationManager.ConnectionStrings[0].ConnectionString;
connection.Open();
}
}
public void CloseConnection()
{
if (connection != null && connection.State != ConnectionState.Closed)
connection.Close();
}
public DataTable ExecuteToDataTable(string sql)
{
DataTable data;
SqlCommand command = null;
SqlDataAdapter adapter = null;
try
{
if (connection.State != ConnectionState.Open)
OpenConnection();
command = new SqlCommand(sql, connection);
adapter = new SqlDataAdapter(command);
retorno = new DataTable();
adapter.Fill(data);
}
finally
{
if (command != null)
command.Dispose();
if (adapter != null)
adapter.Dispose();
CloseConnection();
}
return data;
}
public int ExecuteNonQuery(string sql)
{
SqlCommand command = null;
try
{
if (connection.State != ConnectionState.Open)
OpenConnection();
command = new SqlCommand(sql, connection);
return command.ExecuteNonQuery();
}
finally
{
if (command != null)
command.Dispose();
CloseConnection();
}
}
public object ExecuteScalar(string sql)
{
SqlCommand command = null;
try
{
if (connection.State != ConnectionState.Open)
OpenConnection();
command = new SqlCommand(sql, connection);
return command.ExecuteScalar();
}
finally
{
if (command != null)
command.Dispose();
CloseConnection();
}
}
}
Sample usage:
SqlHelper sql = new SqlHelper();
DataTable data = sql.ExecuteToDataTable("SELECT * FROM Customers");
int affected = sql.ExecuteNonQuery("INSERT Customers VALUES ('Test')");
But if you really want static (if you is on a single user enviroment), just put static on all methods.
I haven't accessed data using SqlCommand etc. for a while as I tend to use NHibernate these days. I am just wondering whether the following code could be improved. I have tried to use best practises (after some google-ing) and potential exceptions are caught at a higher layer.
[WebMethod]
public XmlDocument GetClassRegistrationReport()
{
XmlDocument doc = new XmlDocument();
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["bla"].ToString()))
{
using (SqlCommand command = connection.CreateCommand())
{
command.CommandText = "bla";
command.CommandType = CommandType.StoredProcedure;
connection.Open();
doc.Load(command.ExecuteXmlReader());
}
}
return doc;
}
Thanks!
Best wishes,
Christian
There are a few ways you could improve it a little:
Although the WebMethod pulls data and returns it verbatim with no input parameters, I would suggest seperating service interface and the data into seperate classes. It may make things easier to maintain at a later date.
Assuming there are other DB calls in your framework you may want to consider a helper method in your data layer that wraps up the invocation of a stored procedure. This way you only have one method that all SP calls filter down into which again will make things easier to maintain in the future.
Make the 'bla' key for your connection string setting a constant, this way you can easily reuse and change.
The same applies to the name of the stored procedure, alternatively make it part of your web.config - this means you can change the stored proc name without having to recompile.
If an exception is throw there is no handling for this so the exception will bubble out to the caller, consider catching and handling/logging exceptions. That said you do mention that you are handling exceptions at a higher layer, so I assume this is being done in whatever is calling your webservices.
You should be disposing the SQL command object (in the finally of the try/catch/finally if you do implement exception handling)
EDIT : Code Sample
public class MyWebService
{
[WebMethod]
public XmlDocument GetClassRegistrationReport()
{
return DataLayer.GetClassRegistrationReport();
}
}
// Notice that this is a static internal class, internal to hide the
// data access class from everything but this library and static because
// we don't need instances and using statics will optimise a little.
internal static class DataLayer
{
private const string SP_GetRegistrationReport = "GetRegistrationReport";
private const string Config_DBConnectionString = "PrimaryDB";
private static string GetDB
{
get
{
string dbConnectionString = ConfigurationManager.ConnectionStrings[Config_DBConnectionString].ConnectionString;
if (string.IsNullOrEmpty(dbConnectionString))
{
// This error should could/should be in a resource file.
throw new ConfigurationException("Database connection string is not defined");
}
return dbConnectionString;
}
}
internal static XmlDocument GetClassRegistrationReport()
{
XmlDocument doc = new XmlDocument();
using (SqlConnection connection = new SqlConnection())
{
using (SqlCommand command = connection.CreateCommand())
{
command.CommandText = SP_GetRegistrationReport;
command.CommandType = CommandType.StoredProcedure;
connection.Open();
doc.Load(command.ExecuteXmlReader());
}
}
return doc;
}
}