I am using EF 5.0 and have a question on making the Database calls asynchronous.
To begin with below is the autogenerated method call in contextModel>.context.cs
public virtual ObjectResult<InstructorsComplex> GetInstructors(string nm, string cd, string grp_cd)
{
var nmParameter = nm != null ?
new ObjectParameter("nm", nm) :
new ObjectParameter("nm", typeof(string));
var cdParameter = cd != null ?
new ObjectParameter("cd", cd) :
new ObjectParameter("cd", typeof(string));
var grp_cdParameter = grp_cd != null ?
new ObjectParameter("grp_cd", grp_cd) :
new ObjectParameter("grp_cd", typeof(string));
return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<InstructorsComplex>("GetInstructors", nmParameter, cdParameter, grp_cdParameter);
}
I am calling the method as below to achieve asynchrony since above call takes about 1 second to execute:
public async Task<IList<Instructor>> GetInstructors(DatabaseRequest input)
{
//fetch from database ASYNChronously
var daoOutput = await Task.Run( () => _DAO.GetInstructors(input));
var retVal = daoOutput.ToList<Instructor>();
return retVal;
}
But would it give any kind of performance boost just by running the process using Task.Run() ?
In .Net framework we have xxxAsync() methods. But I don't find any such methods in EF 5.0.
If above code is not efficient, how can I write a asynchronous method for expensive database calls using EF 5.0 ?
Any help is appreciated.
Related
I have 2 system which can communicate through API each other.
Here is my code
System A:
using (var transaction = new TransactionScope())
{
var myBook = _bookRepository.Table.FirstOrDefault(x => x.Id == request.bookID);
myBook.AssigneeId = null;
_bookRepository.Update(ticket);
var result = await _anotherBApi.ApproveBookAsync(request.bookID);
if (result.ShStatus != ResponseStatus.Success)
{
result.ErrorType = ErrorType.Error;
return result;
}
transaction.Complete();
}
Function ApproveBookAsync(request.bookID) will call to B system's API. After handling, B system call back A system's API to update Book's information (the same the one above).
Above my code. I cannot transaction.Complete(); because when B system call A system's API it will create new transaction.
Expect: I want to handle step by step as:
Update new information for a Book instance (sample ID = 1)
Call to B system's API (after B system also call A system's A to update Book ID = 1)
When call B system fail, I want to rollback all changes before. If success, commit.
When using async/await in TransactionScope block, you need to opt that you need your transaction to flow accross thread continuations like this:
using (var transaction = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled))
{
// Your code that contains some calls to async method.
transaction.Complete();
}
I am using EntityFramework Core commands to migration database. The command I am using is like the docs suggests: dnx . ef migration apply. The problem is when specifying AttachDbFileName in connection string, the following error appear: Unable to Attach database file as database xxxxxxx. This is the connection string I am using:
Data Source=(LocalDB)\mssqllocaldb;Integrated Security=True;Initial Catalog=EfGetStarted2;AttachDbFileName=D:\EfGetStarted2.mdf
Please help how to attach the db file to another location.
Thanks
EF core seem to have troubles with AttachDbFileName or doesn't handle it at all.
EnsureDeleted changes the database name to master but keeps any AttachDbFileName value, which leads to an error since we cannot attach the master database to another file.
EnsureCreated opens a connection using the provided AttachDbFileName value, which leads to an error since the file of the database we want to create does not yet exist.
EF6 has some logic to handle these use cases, see SqlProviderServices.DbCreateDatabase, so everything worked quite fine.
As a workaround I wrote some hacky code to handle these scenarios:
public static void EnsureDatabase(this DbContext context, bool reset = false)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
if (reset)
{
try
{
context.Database.EnsureDeleted();
}
catch (SqlException ex) when (ex.Number == 1801)
{
// HACK: EF doesn't interpret error 1801 as already existing database
ExecuteStatement(context, BuildDropStatement);
}
catch (SqlException ex) when (ex.Number == 1832)
{
// nothing to do here (see below)
}
}
try
{
context.Database.EnsureCreated();
}
catch (SqlException ex) when (ex.Number == 1832)
{
// HACK: EF doesn't interpret error 1832 as non existing database
ExecuteStatement(context, BuildCreateStatement);
// this takes some time (?)
WaitDatabaseCreated(context);
// re-ensure create for tables and stuff
context.Database.EnsureCreated();
}
}
private static void WaitDatabaseCreated(DbContext context)
{
var timeout = DateTime.UtcNow + TimeSpan.FromMinutes(1);
while (true)
{
try
{
context.Database.OpenConnection();
context.Database.CloseConnection();
}
catch (SqlException)
{
if (DateTime.UtcNow > timeout)
throw;
continue;
}
break;
}
}
private static void ExecuteStatement(DbContext context, Func<SqlConnectionStringBuilder, string> statement)
{
var builder = new SqlConnectionStringBuilder(context.Database.GetDbConnection().ConnectionString);
using (var connection = new SqlConnection($"Data Source={builder.DataSource}"))
{
connection.Open();
using (var command = connection.CreateCommand())
{
command.CommandText = statement(builder);
command.ExecuteNonQuery();
}
}
}
private static string BuildDropStatement(SqlConnectionStringBuilder builder)
{
var database = builder.InitialCatalog;
return $"drop database [{database}]";
}
private static string BuildCreateStatement(SqlConnectionStringBuilder builder)
{
var database = builder.InitialCatalog;
var datafile = builder.AttachDBFilename;
var dataname = Path.GetFileNameWithoutExtension(datafile);
var logfile = Path.ChangeExtension(datafile, ".ldf");
var logname = dataname + "_log";
return $"create database [{database}] on primary (name = '{dataname}', filename = '{datafile}') log on (name = '{logname}', filename = '{logfile}')";
}
It's far from nice, but I'm using it for integration testing anyway. For "real world" scenarios using EF migrations should be the way to go, but maybe the root cause of this issue is the same...
Update
The next version will include support for AttachDBFilename.
There may be a different *.mdf file already attached to a database named EfGetStarted2... Try dropping/detaching that database then try again.
You might also be running into problems if the user LocalDB is running as doesn't have correct permissions to the path.
I have the following Scenario:
I have 2 web api functions, which delete / insert data into a SQL Server database. The data Access is handled via .net entityframework v6. The insert / delete methods were only called from a local running c# program. I am using HttpClient class to call the web api methods. The web methods works as follows, when I call insert all existing records will be deleted and the new ones will be inserted, so there is no real update process.
Here are my 2 functions:
[HttpDelete()]
public async Task<int> DeleteStartlist(int eventid, int run, int heat, string category)
{
_data.dbsStartlistEntries.RemoveRange(_data.dbsStartlistEntries.Where(s => s.Event.Id == eventid && s.RoundOrder == run && s.HeatOrder == heat && s.Category == category));
return await _data.SaveChangesAsync();
}
[HttpPost()]
public async Task<int> UpdateStartlists(int eventid, List<StartlistEntry> en)
{
try
{
if (en.Count == 0)
return 0;
var xdel = await DeleteStartlist(eventid, en[0].RoundOrder, en[0].HeatOrder, en[0].Category);
var ev = await _data.dbsEvents.FindAsync(eventid);
if (ev != null)
{
en.ForEach(e => e.Event = ev);
_data.dbsStartlistEntries.AddRange(en);
}
return await _data.SaveChangesAsync();
}
catch (System.Exception ex)
{
return 1;
}
}
But now I have the following Problem. For example when I call the Update Method 10 times in a row without waiting between the function calls I receive following exception:
Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.
For me this sounds like a concurrency Problem, but I do not really know how to solve it.
So here is my question, is there a way to let the api calls wait for each other server side, or are they always running concurrent or is there a way to lock the database?
I'm in ASP.NET MVC and am (mostly) using Entity Framework. I want to call a stored procedure without waiting for it to finish. My current approach is to use a background worker. Trouble is, it works fine without using the background worker, but fails to execute with it.
In the DoWork event handler when I call
command.ExecuteNonQuery();
it just "disappears" (never gets to next line in debug mode).
Anyone have tips on calling a sproc asynchronously? BTW, it'll be SQL Azure in production if that matters; for now SQL Server 2008.
public void ExecAsyncUpdateMemberScoreRecalc(MemberScoreRecalcInstruction instruction)
{
var bw = new BackgroundWorker();
bw.DoWork += new DoWorkEventHandler(AsyncUpdateMemberScoreRecalc_DoWork);
bw.WorkerReportsProgress = false;
bw.WorkerSupportsCancellation = false;
bw.RunWorkerAsync(instruction);
}
private void AsyncUpdateMemberScoreRecalc_DoWork(object sender, DoWorkEventArgs e)
{
var instruction = (MemberScoreRecalcInstruction)e.Argument;
string connectionString = string.Empty;
using (var sprocEntities = new DSAsyncSprocEntities()) // getting the connection string
{
connectionString = sprocEntities.Connection.ConnectionString;
}
using (var connection = new EntityConnection(connectionString))
{
connection.Open();
EntityCommand command = connection.CreateCommand();
command.CommandText = DSConstants.Sproc_MemberScoreRecalc;
command.CommandType = CommandType.StoredProcedure;
command.Parameters.AddWithValue(DSConstants.Sproc_MemberScoreRecalc_Param_SageUserId, instruction.SageUserId);
command.Parameters.AddWithValue(DSConstants.Sproc_MemberScoreRecalc_Param_EventType, instruction.EventType);
command.Parameters.AddWithValue(DSConstants.Sproc_MemberScoreRecalc_Param_EventCode, instruction.EventCode);
command.Parameters.AddWithValue(DSConstants.Sproc_MemberScoreRecalc_Param_EventParamId, instruction.EventParamId);
int result = 0;
// NEVER RETURNS FROM RUNNING NEXT LINE (and never executes)... yet it works if I do the same thing directly in the main thread.
result = command.ExecuteNonQuery();
}
}
Add a try catch around the call and see if any exceptions are caught and are thus aborting the thread.
try {
result = command.ExecuteNonQuery();
} catch(Exception ex) {
// Log this error and if needed handle or
throw;
}
I was reading an article in MSDN several months ago and have recently started using the following snippet to execute ADO.NET code, but I get the feeling it could be bad. Am I over reacting or is it perfectly acceptable?
private void Execute(Action<SqlConnection> action)
{
SqlConnection conn = null;
try {
conn = new SqlConnection(ConnectionString);
conn.Open();
action.Invoke(conn);
} finally {
if (conn != null && conn.State == ConnectionState.Open) {
try {
conn.Close();
} catch {
}
}
}
}
public bool GetSomethingById() {
SomeThing aSomething = null
bool valid = false;
Execute(conn =>
{
using (SqlCommand cmd = conn.CreateCommand()) {
cmd.CommandText = ....
...
SqlDataReader reader = cmd.ExecuteReader();
...
aSomething = new SomeThing(Convert.ToString(reader["aDbField"]));
}
});
return aSomething;
}
What is the point of doing that when you can do this?
public SomeThing GetSomethingById(int id)
{
using (var con = new SqlConnection(ConnectionString))
{
con.Open();
using (var cmd = con.CreateCommand())
{
// prepare command
using (var rdr = cmd.ExecuteReader())
{
// read fields
return new SomeThing(data);
}
}
}
}
You can promote code reuse by doing something like this.
public static void ExecuteToReader(string connectionString, string commandText, IEnumerable<KeyValuePair<string, object>> parameters, Action<IDataReader> action)
{
using (var con = new SqlConnection(connectionString))
{
con.Open();
using (var cmd = con.CreateCommand())
{
cmd.CommandText = commandText;
foreach (var pair in parameters)
{
var parameter = cmd.CreateParameter();
parameter.ParameterName = pair.Key;
parameter.Value = pair.Value;
cmd.Parameters.Add(parameter);
}
using (var rdr = cmd.ExecuteReader())
{
action(rdr);
}
}
}
}
You could use it like this:
//At the top create an alias
using DbParams = Dictionary<string, object>;
ExecuteToReader(
connectionString,
commandText,
new DbParams() { { "key1", 1 }, { "key2", 2 } }),
reader =>
{
// ...
// No need to dispose
}
)
IMHO it is indeed a bad practice, since you're creating and opening a new database-connection for every statement that you execute.
Why is it bad:
performance wise (although connection pooling helps decrease the performance hit): you should open your connection, execute the statements that have to be executed, and close the connection when you don't know when the next statement will be executed.
but certainly context-wise. I mean: how will you handle transactions ? Where are your transaction boundaries ? Your application-layer knows when a transaction has to be started and committed, but you're unable to span multiple statements into the same sql-transaction with this way of working.
This is a very reasonable approach to use.
By wrapping your connection logic into a method which takes an Action<SqlConnection>, you're helping prevent duplicated code and the potential for introduced error. Since we can now use lambdas, this becomes an easy, safe way to handle this situation.
That's acceptable. I've created a SqlUtilities class two years ago that had a similar method. You can take it one step further if you like.
EDIT: Couldn't find the code, but I typed a small example (probably with many syntax errors ;))
SQLUtilities
public delegate T CreateMethod<T> (SqlDataReader reader);
public static T CreateEntity<T>(string query, CreateMethod<T> createMethod, params SqlParameter[] parameters) {
// Open the Sql connection
// Create a Sql command with the query/sp and parameters
SqlDataReader reader = cmd.ExecuteReader();
return createMethod(reader);
// Probably some finally statements or using-closures etc. etc.
}
Calling code
private SomeThing Create(SqlDataReader reader) {
SomeThing something = new SomeThing();
something.ID = Convert.ToIn32(reader["ID"]);
...
return something;
}
public SomeThing GetSomeThingByID (int id) {
return SqlUtilities.CreateEntity<SomeThing> ("something_getbyid", Create, ....);
}
Of course you could use a lambda expression instead of the Create method, and you could easily make a CreateCollection method and reuse the existing Create method.
However if this is a new project. Check out LINQ to entities. Is far easier and flexible than ADO.Net.
Well, In my opinion check what you do before going through it.Something that is working doesn't mean it is best and good programming practice.Check out and find a concrete example and benefit of using it.But if you are considering using for big projects it would be nice using frameworks like NHibernate.Because there are a lot projects even frameworks developed based on it,like http://www.cuyahoga-project.org/.