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Error in Using SaveChanges() Method with EF core

In the following code, I receive an error in _context.SaveChanges(); when adding a new record to FeedbackComments inside the first foreach loop. The error is New transaction is not allowed because there are other threads running in the session.. Any ideas why this is happening?
BTW, I keep receiving the same error when SaveChanges is called only once after the outer loop.
List<FeedbackComment> feedbackComments = comments.Select(c => new FeedbackComment
{
Id = c.Id,
CommentText = c.Content,
SubmissionId = submissionId,
UserDisplayName = c.Author.DisplayName,
DateCreated = c.CreatedTime.GetValueOrDefault(),
FeedbackReplies = c.Replies.Select(r => new FeedbackReply
{
Id = r.Id,
UserDisplayName = r.Author.DisplayName,
ReplyText = r.Content,
DateCreated = r.CreatedTime.GetValueOrDefault(),
FeedbackCommentId = c.Id
}).ToList()
}).ToList();
_context.SaveChanges();
foreach (FeedbackComment c in feedbackComments)
{
if (!_context.FeedbackComments.Any(fc => fc.Id == c.Id))
{
ApplicationUser commentOwner = _context.ApplicationUsers.FirstOrDefault(au => au.GoogleDisplayName == c.UserDisplayName);
if(commentOwner != null)
{
c.UserId = commentOwner.Id;
_context.FeedbackComments.Add(c);
newComments = true;
_context.SaveChanges();
}
}
foreach (FeedbackReply r in c.FeedbackReplies)
{
if (!_context.FeedbackReplies.Any(fr => fr.Id == r.Id))
{
ApplicationUser replyOwner = _context.ApplicationUsers.FirstOrDefault(au => au.GoogleDisplayName == c.UserDisplayName);
if (replyOwner != null)
{
r.UserId = replyOwner.Id;
_context.FeedbackReplies.Add(r);
newComments = true;
_context.SaveChanges();
}
}
}
}

When you are trying to save a change using a transaction, you should wait until any other transactions are completed. On the other hand, waiting for the previous transaction to be completed, makes severe performance issue.
You should put _context.SaveChanges(); outside the foreach loop like this:
foreach (FeedbackReply r in c.FeedbackReplies)
{
if (!_context.FeedbackReplies.Any(fr => fr.Id == r.Id))
{
ApplicationUser replyOwner = _context.ApplicationUsers.FirstOrDefault(au => au.GoogleDisplayName == c.UserDisplayName);
if (replyOwner != null)
{
r.UserId = replyOwner.Id;
_context.FeedbackReplies.Add(r);
newComments = true;
}
}
}
_context.SaveChanges();
In the above code, all changes are applied to the database in one transaction.

Why are you calling SaveChanges after the initial data fetch? If you leave that one out and call SaveChanges only once, at the end, it should work, as Hadi said.

Entity Framework inserts only one record

I'm saving a record in my database by passing 3 parameters, the number parameter is passed to pick the number of records from one table to another table. However the loop written inserts only 1 record instead of the number parameter passed.
I'm using the the Take() method in Entity Framework to pick the records. It inserts only the last records in the loop
public async Task<bool> Save(string company, int number, string registrationNumber)
{
using (var trans = _dbContext.Database.BeginTransaction())
{
var db = new SibaCiidDbContext();
var dbSet = _dbContext.Set<IntermediaryAssignment>();
// pick number of records
var data = await (from s in db.StickerDistributions
where s.Dispatched == false &&
s.CompanyCode == company
select s).Take(number).ToListAsync();
var intermediary = (await _repo.FindBy(s => s.RegistrationNumber == registrationNumber &&
s.Status == EntityStatus.Active)).FirstOrDefault();
var entity = new IntermediaryAssignment();
foreach (var sticker in data)
{
entity.CompanyCode = sticker.CompanyCode;
entity.StickerCode = sticker.StickerCode;
entity.RegistrationNumber = intermediary.RegistrationNumber;
entity.Status = EntityStatus.Active;
entity.CreatedDate = DateTime.Now;
entity.Dispatched = false;
entity.IntermediaryType = intermediary.IntermediaryType;
dbSet.Add(entity);
}
trans.Commit();
return await _dbContext.SaveChangesAsync() > 0;
}
}

You are creating one entity, and then updating it 3 times. You need to create a new entity for each new record.
Move the new IntermediaryAssignment() inside the loop.
foreach (var sticker in data)
{
var entity = new IntermediaryAssignment();
entity.CompanyCode = sticker.CompanyCode;
entity.StickerCode = sticker.StickerCode;
entity.RegistrationNumber = intermediary.RegistrationNumber;
entity.Status = EntityStatus.Active;
entity.CreatedDate = DateTime.Now;
entity.Dispatched = false;
entity.IntermediaryType = intermediary.IntermediaryType;
dbSet.Add(entity);
}

Object multiple reference IEntityTracker error while saving audit table

first I know this question has been asked but I really couldn't find an answer nor find the root of the problem so maybe a someone points me in the right direction.
I'm having the An entity object cannot be referenced by multiple instances of IEntityChangeTracker. error when trying to save into the log tables.
for the log table, I'm using
https://github.com/thepirat000/Audit.NET/tree/master/src/Audit.EntityFramework
so inside my DbContext class where I define the dbset, I have to override the onscopecreated function
the problem here is that when context.Savechanges run for the first audit record for each table it works but after first record, I get the multiple reference error.
so let's say I have the following tables
Languages table. with the following values
English,French,German
Countries Table with the following values
UK,France,Germany
for languages table, if I change English to English3 and save it works It records to the audit table but then for languages table, I can not do any changes at any records it's the same in every table
what am I missing?
private void SaveToLogTable(AuditScope auditScope)
{
foreach (var entry in ((AuditEventEntityFramework)auditScope.Event).EntityFrameworkEvent.Entries)
{
if(entry.Action is null) return;
if (TABLES.Any(x => x.T_TABLE_NAME.Equals(entry.Table)))
{
var newLog = new LOGS
{
LOG_ACTION = ACTIONS.FirstOrDefault(x => x.A_DESC == entry.Action)?.A_CODE,
LOG_DATE = DateTime.Now,
USERS = MyGlobalSettings.MyUser
};
if (entry.Changes != null)
{
foreach (var changes in entry.Changes)
{
var ch = new CHANGES
{
CH_COLUMN = changes.ColumnName,
CH_NEW_VALUE = changes.NewValue.ToString(),
CH_ORIGINAL_VALUE = changes.OriginalValue.ToString()
};
newLog.CHANGES.Add(ch);
}
}
if (entry.ColumnValues != null)
{
foreach (var kv in entry.ColumnValues)
{
var val = new VALUES
{
ColumnName = kv.Key,
ColumnValue = kv.Value.ToString()
};
newLog.VALUES.Add(val);
}
}
TABLES.First(x => x.T_TABLE_NAME.Equals(entry.Table)).LOGS.Add(newLog);
}
else
{
var table = new TABLES {T_TABLE_NAME = entry.Table};
var newLog = new LOGS
{
LOG_ACTION = ACTIONS.FirstOrDefault(x => x.A_DESC.Equals(entry.Action))?.A_CODE,
LOG_DATE = DateTime.Now,
LOG_USER_REFNO = MyGlobalSettings.MyUser.U_ROWID
//USERS = MyGlobalSettings.MyUser
};
if (entry.Changes != null)
{
foreach (var changes in entry.Changes)
{
var ch = new CHANGES
{
CH_COLUMN = changes.ColumnName,
CH_NEW_VALUE = changes.NewValue.ToString(),
CH_ORIGINAL_VALUE = changes.OriginalValue.ToString()
};
newLog.CHANGES.Add(ch);
}
}
if (entry.ColumnValues != null)
{
foreach (var kv in entry.ColumnValues)
{
var val = new VALUES
{
ColumnName = kv.Key,
ColumnValue = kv.Value is null? "": kv.Value.ToString()
};
newLog.VALUES.Add(val);
}
}
table.LOGS.Add(newLog);
//TABLES.Attach(table);
//TABLES.First(x => x.T_TABLE_NAME.Equals(entry.Table)).LOGS.Add(newLog);
TABLES.Add(table);
//TablesList.Add(table);
}
//entry.Entity
}
}

Getting double data in DB

I pull student data from 2 databases. 1 from an online SOAP API which can handle async calls and 1 from a local DB with an older services that doesnt support async.
I compare these databases and write the differences in a local sqlDB through EF.
Problem:
I get double entries in my EF DB. He puts the correct data and amount in arrays inside the method, but it looks like once he hits the db.savechanges() he jumps back up a few line and saves again.
I don't even know where this extra thread comes from.
Some code might be still there from numerous tries to solve it. For instance I tried with addrange but I get an error when he tries to add the FullVarianceList.
public async Task<bool> FullStudentCompare(string date) //format DD/MM/YYYY
{
try
{
//DB context
using (var db = new SchoolDbContext())
{
//GET DATA
//SMT (async)
List<SmtStudent> smtStdudentList = await GetAllSmartschoolStudents();
//Wisa (sync)
//on date, or if emty on current systemdate
List<WisaStudent> wisaList;
if (date == "")
{
wisaList = GetWisaStudentData(DateTime.Now.ToShortDateString());
}
else
{
wisaList = GetWisaStudentData(date);
}
//Flags and props needed for DB entry after compare
bool existsInLocalDb = false;
List<Variance> vList = new List<Variance>();
//Full list to add to DB outside foreach
List<Variance> fullVarianceList = new List<Variance>();
//Full List of new Students to write to DB outside foreach
List<DbStudent> fullStudentList = new List<DbStudent>();
//Compare lists
foreach (WisaStudent wstd in wisaList)
{
//determine correct classCode
string klasCode;
if (wstd.klasgroep.Trim() == "Klasgroep 00")
{
klasCode = wstd.klas.Trim();
}
else
{
klasCode = wstd.klasgroep.Trim();
}
//Create SmtStudent object for compare
SmtStudent tempStd = new SmtStudent(true,
wstd.voornaam.Trim(),
wstd.naam.Trim(),
wstd.stamboeknummer.Trim(),
wstd.geslacht.Trim(),
wstd.geboortedatum.Trim(),
wstd.straat.Trim(),
wstd.huisnummer.Trim(),
wstd.busnummer.Trim(),
wstd.postcode.Trim(),
wstd.gemeente.Trim(),
wstd.emailadres.Trim(),
wstd.GSM_nummer.Trim(),
wstd.levensbeschouwing.Trim(),
wstd.coaccountmoedervoornaam.Trim(),
wstd.coaccountmoedernaam.Trim(),
wstd.coaccountmoederemailadres.Trim(),
wstd.coaccountmoederGSM_nummer.Trim(),
wstd.coaccountvadervoornaam.Trim(),
wstd.coaccountvadernaam.Trim(),
wstd.coaccountvaderemailadres.Trim(),
wstd.coaccountvaderGSM_nummer.Trim(),
klasCode,
wstd.nationaliteit,
wstd.geboorteGemeente,
wstd.geboorteLand
);
//Find matching SmtStudent
SmtStudent smtStd = smtStdudentList.Find(i => i.Internnummer == wstd.stamboeknummer);
//Find matching Std in local DB
DbStudent dbStd = await db.Students.Where(i => i.Stamboeknummer == wstd.stamboeknummer).FirstOrDefaultAsync();
//if none exists in the local DB create an entity to update and write to DB
if (dbStd == null)
{
dbStd = new DbStudent(wstd.voornaam.Trim(),
wstd.naam.Trim(),
wstd.stamboeknummer.Trim(),
wstd.geslacht.Trim(),
wstd.geboortedatum.Trim(),
wstd.straat.Trim(),
wstd.huisnummer.Trim(),
wstd.busnummer.Trim(),
wstd.postcode.Trim(),
wstd.gemeente.Trim(),
wstd.emailadres.Trim(),
wstd.GSM_nummer.Trim(),
wstd.levensbeschouwing.Trim(),
wstd.coaccountmoedervoornaam.Trim(),
wstd.coaccountmoedernaam.Trim(),
wstd.coaccountmoederemailadres.Trim(),
wstd.coaccountmoederGSM_nummer.Trim(),
wstd.coaccountvadervoornaam.Trim(),
wstd.coaccountvadernaam.Trim(),
wstd.coaccountvaderemailadres.Trim(),
wstd.coaccountvaderGSM_nummer.Trim(),
klasCode,
wstd.loopbaanDatum,
wstd.nationaliteit,
wstd.geboorteGemeente,
wstd.geboorteLand
);
db.Students.Add(dbStd);
fullStudentList.Add(dbStd);
}
else
{
existsInLocalDb = true;
}
if (smtStd == null)
{
//Std doesn't exist in Smt -> New student
dbStd.IsNewStudent = true;
dbStd.ClassMovement = true;
//remove from wisaList
wisaList.Remove(wstd);
}
else
{
//clear vlist from previous iterations
vList.Clear();
//get all properties on the obj, cycle through them and find differences
PropertyInfo[] props = smtStd.GetType().GetProperties();
vList.AddRange(props.Select(f => new Variance
{
Property = f.Name,
ValueA = f.GetValue(smtStd),
ValueB = f.GetValue(tempStd),
Checked = false
})
.Where(v => !v.ValueA.Equals(v.ValueB) && v.ValueB != null)
.ToList());
//If the users allrdy exists in LocalDb delete all previously recorded variances
if (existsInLocalDb)
{
if (db.Variances.Where(j => j.Student.StudentId.Equals(dbStd.StudentId)).FirstOrDefault() != null)
{ //if the student allready exists we will recreate the variancelist, hence deleting all current items first
List<Variance> existingList = db.Variances.Where(j => j.Student.StudentId.Equals(dbStd.StudentId)).ToList();
foreach (Variance v in existingList)
{
db.Variances.Remove(v);
}
}
}
//Add new variances if vList is not empty
if (vList.Count > 0)
{
//Check if KlasCode is a variance -> set classmovement to true
if (vList.Where(i => i.Property == "KlasCode").FirstOrDefault() != null)
{
dbStd.ClassMovement = true;
}
else
{
dbStd.ClassMovement = false;
}
//add the StudentObject to the variance to link them 1-many
foreach (Variance v in vList)
{
v.Student = dbStd;
fullVarianceList.Add(v);
db.Variances.Add(v);
}
}
}
}
//add the full lists of variances and new students to DB
//db.Variances.AddRange(fullVarianceList);
//db.Students.AddRange(fullStudentList);
db.SaveChanges();
return true;
}
}
catch(Exception ex)
{
return false;
}
}

A couple of things:
It is important to understand that EF uses a unit of work pattern where none of the changes to the entities are persisted until SaveChanges is called which explains the "once he hits the db.Savechanges() he jumps back up" phenomenon.
When you have a 1 to many relationsship and you assign a collection of entities to a navigation property on another entity and then add that parent entity to the DbContext, EF marks those child entities to be added too. In your case dbStd is added at the line "db.Students.Add(dbStd);" and at the line "v.Student = dbStd;". This is most likely what is causing your duplicates.

SQL Server CE EF Optimization

I have the following code which updates / adds data to a SQL Server CE database with EF6, which is working fine for small number of records. However when the volume of records exceeds 1000~2000 the transaction become very slow (10~15sec). Is there any way to optimize it?
Database.DefaultConnectionFactory = new SqlCeConnectionFactory("System.Data.SqlServerCe.4.0", "", MyProject.ConnectionString);
ProjectContext context = new ProjectContext();
context.Configuration.AutoDetectChangesEnabled = false;
context.Configuration.ValidateOnSaveEnabled = false;
using (var db = new ProjectContext())
{
foreach (var item in MyProject.Brands)
{
if (!db.Brands.Any(i => i.Name == item.Name))
{
// Add
db.Brands.Add(item);
}
else
{
// Update
var found = db.Brands.First(i => i.Name == item.Name);
found = item;
}
}
db.SaveChangesAsync();

This way you save 50% on your Linq queries, and your update might actually work (your MyProject.Brands are not attached in any way to your new ProjectContext that you are using, the found that you extract from there is attached, but in your original code, you overwrote it with yuor item, meaning it will be ignored.
context I have left out completely, as you were not doing anything with it, as your using creates a new ProjectContext anyway.
using (var db = new ProjectContext())
{
foreach (var item in MyProject.Brands)
{
var found = db.Brands.FirstOrdefault(i => i.Name == item.Name);
if (found == null)
{
// Add
db.Brands.Add(item);
}
else
{
// Update
found.prop1 = item.prop1;
found.prop2 = item.prop2;
// ... etc, for all and any updatable properties
}
}
db.SaveChangesAsync();
}