I have a very strange error with dapper:
there is already an open DataReader associated with this Command
which must be closed first
But I don't use DataReader! I just call select query on my server application and take first result:
//How I run query:
public static T SelectVersion(IDbTransaction transaction = null)
{
return DbHelper.DataBase.Connection.Query<T>("SELECT * FROM [VersionLog] WHERE [Version] = (SELECT MAX([Version]) FROM [VersionLog])", null, transaction, commandTimeout: DbHelper.CommandTimeout).FirstOrDefault();
}
//And how I call this method:
public Response Upload(CommitRequest message) //It is calling on server from client
{
//Prepearing data from CommitRequest
using (var tr = DbHelper.DataBase.Connection.BeginTransaction(IsolationLevel.Serializable))
{
int v = SelectQueries<VersionLog>.SelectVersion(tr) != null ? SelectQueries<VersionLog>.SelectVersion(tr).Version : 0; //Call my query here
int newVersion = v + 1; //update version
//Saving changes from CommitRequest to db
//Updated version saving to base too, maybe it is problem?
return new Response
{
Message = String.Empty,
ServerBaseVersion = versionLog.Version,
};
}
}
}
And most sadly that this exception appearing in random time, I think what problem in concurrent access to server from two clients.
Please help.
This some times happens if the model and database schema are not matching and an exception is being raised inside Dapper.
If you really want to get into this, best way is to include dapper source in your project and debug.
Related
I'm trying to do a select count query in Sql Server using Dapper. The expected response should be 0 when a profile does not exist. When I do the query in SSMS it returns correctly, but in the API using Dapper it returns 1. Any idea why this is happening?
public IActionResult GetProfileCount(string profileId)
{
int profileCount = 0;
using (IDbConnection db = new SqlConnection(connectionString))
{
try
{
profileCount = db.Query($"select count(*) from Profile where Id='{profileId}'").Count();
}
catch(Exception ex)
{
Console.WriteLine($"Error retrieving count for ProfileId: {profileId}", ex.Message);
}
}
return Ok(profileCount);
}
I see you added your own answer but could I recommend not doing it that way. When you do
profileCount = db.Query($"select * from Profile where Id='{profileId}'").Count();
What you are actually doing is selecting every field from the database, pulling it into your C# application, and then counting how many results you got back. Then you are binning all that data you got back, very inefficient!
Change it to this :
profileCount = db.QueryFirst<int>($"select count(*) from Profile where Id = #profileId", new { profileId })");
Instead you are selecting an "int" from the result set, which just so happens to be your count(*). Perfect!
More on querying in Dapper here : https://dotnetcoretutorials.com/2019/08/05/dapper-in-net-core-part-2-dapper-query-basics/
Also notice that (similar to the other answer), I am using parameterized queries. I also heavily recommend this as it protects you from SQL Injection. Your initial example is very vulnerable!
You can read a little more about SQL Injection in C#/MSSQL here https://dotnetcoretutorials.com/2017/10/11/owasp-top-10-asp-net-core-sql-injection/ But just know that Dapper protects you from it as long as you use the inbuilt helpers to add parameters to your queries.
Another option is use the method ExecuteScalar for "select count" queries:
profileCount = db.ExecuteScalar<int>("select count(*) from Profile where Id=#profileId", new { profileId });
Ref.: https://www.learndapper.com/selecting-scalar-values
Try and change your query to the following:
db.Query($"select count(*) from Profile where Id = #ProfileId", new { ProfileId = profileId }).Count()
I figured it out. The .Count() is counting the rows of the result, which is going to be 1 because the result is one row displaying the number 0. I switched my code to this and it works now.
public IActionResult GetProfileCount(string profileId)
{
int profileCount = 0;
using (IDbConnection db = new SqlConnection(connectionString))
{
try
{
profileCount = db.Query($"select * from Profile where Id='{profileId}'").Count();
}
catch(Exception ex)
{
Console.WriteLine($"Error retrieving count for ProfileId: {profileId}", ex.Message);
}
}
return Ok(profileCount);
}
_context.Update(v) ;
_context.SaveChanges();
When I use this code then SQL Server adds a new record instead of updating the
current context
[HttpPost]
public IActionResult PageVote(List<string> Sar)
{
string name_voter = ViewBag.getValue = TempData["Namevalue"];
int count = 0;
foreach (var item in Sar)
{
count = count + 1;
}
if (count == 6)
{
Vote v = new Vote()
{
VoteSarparast1 = Sar[0],
VoteSarparast2 = Sar[1],
VoteSarparast3 = Sar[2],
VoteSarparast4 = Sar[3],
VoteSarparast5 = Sar[4],
VoteSarparast6 = Sar[5],
};
var voter = _context.Votes.FirstOrDefault(u => u.Voter == name_voter && u.IsVoted == true);
if (voter == null)
{
v.IsVoted = true;
v.Voter = name_voter;
_context.Add(v);
_context.SaveChanges();
ViewBag.Greeting = "رای شما با موفقیت ثبت شد";
return RedirectToAction(nameof(end));
}
v.IsVoted = true;
v.Voter = name_voter;
_context.Update(v);
_context.SaveChanges();
return RedirectToAction(nameof(end));
}
else
{
return View(_context.Applicants.ToList());
}
}
You need to tell the DbContext about your entity. If you do var vote = new Vote() vote has no Id. The DbContext see this and thinks you want to Add a new entity, so it simply does that. The DbContext tracks all the entities that you load from it, but since this is just a new instance, it has no idea about it.
To actually perform an update, you have two options:
1 - Load the Vote from the database in some way; If you get an Id, use that to find it.
// Loads the current vote by its id (or whatever other field..)
var existingVote = context.Votes.Single(p => p.Id == id_from_param);
// Perform the changes you want..
existingVote.SomeField = "NewValue";
// Then call save normally.
context.SaveChanges();
2 - Or if you don't want to load it from Db, you have to manually tell the DbContext what to do:
// create a new "vote"...
var vote = new Vote
{
// Since it's an update, you must have the Id somehow.. so you must set it manually
Id = id_from_param,
// do the changes you want. Be careful, because this can cause data loss!
SomeField = "NewValue"
};
// This is you telling the DbContext: Hey, I control this entity.
// I know it exists in the DB and it's modified
context.Entry(vote).State = EntityState.Modified;
// Then call save normally.
context.SaveChanges();
Either of those two approaches should fix your issue, but I suggest you read a little bit more about how Entity Framework works. This is crucial for the success (and performance) of your apps. Especially option 2 above can cause many many issues. There's a reason why the DbContext keep track of entities, so you don't have to. It's very complicated and things can go south fast.
Some links for you:
ChangeTracker in Entity Framework Core
Working with Disconnected Entity Graph in Entity Framework Core
I have custom extractor, and I'm trying to log some messages from it.
I've tried obvious things like Console.WriteLine, but cannot find where output is. However, I found some system logs in adl://<my_DLS>.azuredatalakestore.net/system/jobservice/jobs/Usql/.../<my_job_id>/.
How can I log something? Is it possible to specify log file somewhere on Data Lake Store or Blob Storage Account?
A recent release of U-SQL has added diagnostic logging for UDOs. See the release notes here.
// Enable the diagnostics preview feature
SET ##FeaturePreviews = "DIAGNOSTICS:ON";
// Extract as one column
#input =
EXTRACT col string
FROM "/input/input42.txt"
USING new Utilities.MyExtractor();
#output =
SELECT *
FROM #input;
// Output the file
OUTPUT #output
TO "/output/output.txt"
USING Outputters.Tsv(quoting : false);
This was my diagnostic line from the UDO:
Microsoft.Analytics.Diagnostics.DiagnosticStream.WriteLine(System.String.Format("Concatenations done: {0}", i));
This is the whole UDO:
using System.Collections.Generic;
using System.IO;
using System.Text;
using Microsoft.Analytics.Interfaces;
namespace Utilities
{
[SqlUserDefinedExtractor(AtomicFileProcessing = true)]
public class MyExtractor : IExtractor
{
//Contains the row
private readonly Encoding _encoding;
private readonly byte[] _row_delim;
private readonly char _col_delim;
public MyExtractor()
{
_encoding = Encoding.UTF8;
_row_delim = _encoding.GetBytes("\n\n");
_col_delim = '|';
}
public override IEnumerable<IRow> Extract(IUnstructuredReader input, IUpdatableRow output)
{
string s = string.Empty;
string x = string.Empty;
int i = 0;
foreach (var current in input.Split(_row_delim))
{
using (System.IO.StreamReader streamReader = new StreamReader(current, this._encoding))
{
while ((s = streamReader.ReadLine()) != null)
{
//Strip any line feeds
//s = s.Replace("/n", "");
// Concatenate the lines
x += s;
i += 1;
}
Microsoft.Analytics.Diagnostics.DiagnosticStream.WriteLine(System.String.Format("Concatenations done: {0}", i));
//Create the output
output.Set<string>(0, x);
yield return output.AsReadOnly();
// Reset
x = string.Empty;
}
}
}
}
}
And these were my results found in the following directory:
/system/jobservice/jobs/Usql/2017/10/20.../diagnosticstreams
good question. I have been asking myself the same thing. This is theoretical, but I think it would work (I'll updated if I find differently).
One very hacky way is that you could insert rows into a table with your log messages as a string column. Then you can select those out and filter based on some log_producer_id column. You also get the benefit of logging if part of the script works, but later parts do not assuming the failure does not roll back. Table can be dumped at end as well to file.
For the error cases, you can use the Job Manager in ADLA to open the job graph and then view the job output. The errors often have detailed information for data-related errors (e.g. row number in file with error and a octal/hex/ascii dump of the row with issue marked with ###).
Hope this helps,
J
ps. This isn't a comment or an answer really, since I don't have working code. Please provide feedback if the above ideas are wrong.
I am developing a wcf service for Windows 8 APP. But I'm choked up at one point.
The following method, it is coming data in the database using entity. But this the data returns back to a class type. My question , if result is null what can I sent person who will this method
public AnketorDTO AnketorBul(string tc, string pass)
{
_entity = new AnketDBEntities();
var result = (from i in _entity.Anketors
where i.TC == tc
where i.Sifre == pass
select i).ToList();
if (!result.Any())
-->>> return new AnketorDTO();
Anketor anketor = result.First();
return Converter.ConvertAnketorToAnketorDTO(anketor);
}
with this methot I SENT it by creating a new class type but part which use this methot does not work because the values become null. how can we prevent it.
Client :
AnketorDTO anketor = await client.AnketorBulAsync(txtKullanici.Text, txtSifre.Password);
**if (anketor != null)
lblError.Text = anketor.Adi;**
else
lblError.Text = "Hata";
Can you try this method to see, if it works?
_entity = new AnketDBEntities();
var result = _entity.Anketors.FirstOrDefault(yourexpressions);
I have the following Unit Test method:
void TestOrderItemDelete()
{
using (new SessionScope())
{
var order = Order.FindById(1234);
var originalItemCount = order.OrderItems.Count;
Assert.IsTrue(originalCount > 0);
var itemToDelete = order.OrderItems[0];
itemToDelete.DeleteAndFlush(); // itemToDelete.Delete();
order.Refresh();
Assert.AreEqual(originalCount - 1, order.OrderItems.Count);
}
}
As you can see from the comment after the DeleteAndFlush command, I had to change it from a simple Delete to get the Unit test to pass. Why is this? The same is not true for my other unit test for adding an OrderItem. This works just fine:
void TestOrderItemAdd()
{
using (new SessionScope())
{
var order = Order.FindById(1234);
var originalItemCount = order.OrderItems.Count;
var itemToAdd = new OrderItem();
itemToAdd.Order = order;
itemToAdd.Create(); // Notice, this is not CreateAndFlush
order.Refresh();
Assert.AreEqual(originalCount + 1, order.OrderItems.Count);
}
}
All of this came up when I started using Lazy Instantiation of the Order.OrderItems relationship mapping, and had to add the using(new SessionScope) block around the test.
Any ideas?
This is difficult to troubleshoot without knowing the contents of your mappings, but one possibility is that you have the ID property of the OrderItem mapped using an identity field (or sequence, etc.) in the DB. If this is the case, NHibernate must make a trip to the database in order to generate the ID field, so the OrderItem is inserted immediately. This is not true of a delete, so the SQL delete statement isn't executed until session flush.