this code throw exception while i am trying to update value ,first value only updated and then throw the exception "Collection was modified; enumeration operation may not execute." !!!!
Hashtable hh = new Hashtable();
hh.Add("val 1",null);
hh.Add("val 2", null);
foreach (string dd in hh.Keys)
{
hh[dd] = "some_value";
// MessageBox.Show(dd.Value.ToString());
}
i need to update empty values in hashtables or any equivalent structure that has [key,value]??
You need to make copy of hh.Keys, because you are trying to change Hashtable which is invalid operation while enumerating its keys in the foreach loop.
Try this code
foreach (string dd in new List<object>(hh.Keys.Cast<object>()))
{
hh[dd] = "some_value";
MessageBox.Show(dd);
}
Related
Using Async-based Webservice and Async framework in WinRT (Win8) to get a large recordsets(1000 to 5000) from a remote Ms SQL Server.
I want to know :
1) Which is the best approach to handle to insert large recordsets into SQLite?
2) Using RollBack transaction will start all over again if there is connection error. The below method will insert whatever and I can update the data later if the records are not complete. Is this a good approach?
3) Any better way to enhance my below solution?
This foreach statement to handle
each reords in returned result which returned from Async-Based WebService:
foreach (WebServiceList _List in IList)
{
InsertNewItems(_List.No, _List.Description, _List.Unit_Price, _List.Base_Unit_of_Measure);
}
private void InsertNewItems(string ItemNo, string ItemName, decimal ItemPrice, string ItemBUoM)
{
var existingItem = (db2.Table().Where(c => c.No == ItemNo)).SingleOrDefault();
if (existingItem != null)
{
existingItem.No = ItemNo;
existingItem.Description = ItemName;
existingItem.Unit_Price = ItemPrice;
existingItem.BaseUnitofMeasure = ItemBUoM;
int success = db2.Update(existingItem);
}
else
{
int success = db2.Insert(new Item()
{
No = ItemNo,
Description = ItemName,
Unit_Price = ItemPrice,
Base_Unit_of_Measure = ItemBUoM
});
}
}
You should use RunInTransaction from sqlite-net. The documentation for it says,
Executes action within a (possibly nested) transaction by wrapping it
in a SAVEPOINT. If an exception occurs the whole transaction is rolled
back, not just the current savepoint. The exception is rethrown.
using (var db = new SQLiteConnection(DbPath))
{
db.RunInTransaction(() =>
{
db.InsertOrReplace(MyObj);
});
}
Wiki article for Transactions at GitHub
The most important performance aspect for bulk inserts is to use a single transaction. If you want to handle aborts, I suggest that you feed the data in sufficiently large parts and restart from that point on next time. An SQL transaction either finishes completely or rolls back completely, so unless the input data changes between two runs, there should be no need to do an insert-or-update.
See, for example, here for a discussion of SQLite bulk insert performance using different methods.
I've got the above ring exception in my code. What I try is to use where clause with a list variable and that's why I use Contains method but I keep getting the error and I can't understand what I do wrong
List<string> TouristID = (List<string>)Session["TouristID"];
List<Tourist> customerInterests = (from tourist in db2.Tourist
where (TouristID.Contains(tourist.Tourist_ID.ToString()))
select tourist).ToList();
foreach (var customer in customerInterests)
{
String strName_kir = customer.Name_kir;
String Lastname_kir = customer.Midname_kir;
}
you cannot use .ToString() inside a LinqToSql expression because it will try to translate it to SQL
You cannot use ToString or any other methods that cannot be translated to SQL.
You should be able to do the following:
List<string> TouristID = (List<string>)Session["TouristID"];
//Get them as integers
var touristIds = TouristID.Select(x => int.Parse(x));
List<Tourist> customerInterests = (from tourist in db2.Tourist
where (touristIds.Contains(tourist.Tourist_ID))
select tourist).ToList();
The ToString() method is not evaluated by LinQ to Entities, because it cannot be translated to SQL.
Try to change the type of your list to the destination type or parse them into a new List.
So I have this old code being used, that runs simple ExecuteNonQuery command for database calls. I'm using DbConnection, DbTransaction and other System.Data.Common commands.
I seem to get a lot of Null Reference errors whenever I use the function in certain parts of the project, though it seems fine in other parts. I think it has to do with opening connections manually or some problem with calling it, but I'm wondering if the function itself is badly designed originally (shouldn't there be a way to fix any problems in the way it is called?)
I feel when transactions are involved, these null reference errors come up more often, I think the error I get is null exception at "_command = _db.GetStoredProcCommand(storedProcedure);" inside the following function. But that stored procedure does exist, so it makes no sense.
public List<OutputParameter> execute(String storedProcedure, StoredProcedureParameter[] sqlParameters)
{
try
{
List<OutputParameter> outputParameters = new List<OutputParameter>();
_command = _db.GetStoredProcCommand(storedProcedure);
for (int x = 0; x < sqlParameters.GetLength(0); x++)
{
if (sqlParameters[x] != null)
{
StoredProcedureParameter sqlParameter = sqlParameters[x];
String param = sqlParameter.ParameterName;
DbType dbType = sqlParameter.DbType;
object value = sqlParameter.Value;
if (sqlParameter.IsOutputParam)
{
_db.AddOutParameter(_command, param, dbType, 32);
OutputParameter outputParameter = new OutputParameter(param);
outputParameters.Add(outputParameter);
}
else
_db.AddInParameter(_command, param, dbType, value);
}
}
if (_transaction == null)
_db.ExecuteNonQuery(_command);
else
_db.ExecuteNonQuery(_command, _transaction);
foreach (OutputParameter op in outputParameters)
{
op.ParameterValue = _db.GetParameterValue(_command, op.ParameterName);
}
return outputParameters;
}
catch (SqlException sqle)
{
throw new DataAccessException(sqle.ToString());
}
catch (Exception e)
{
throw new DataAccessException(e.ToString());
}
}
Your _command variable appears to be a field and as such a shared member.
As such your code is very susceptible to multithreading issues (if two functions call this class with different stored procedures, what happens?).
A Command should also be closed and disposed of properly, which is not happening in your code, not explicitly anyways.
If you are getting a null reference exception in the line _command = _db.GetStoredProcCommand(storedProcedure); then the only thing that can be null there is _db. The storedProcedure is just a parameter and _command could happily be null without a problem.
Since you aren't actually doing anything in the code to make sure that _db exists and is valid, open, etc. then this is most likely the problem.
I have the following function in by Data Access Layer but I am receiving the following error on my RETURN statement.
The type arguments for method
'System.Data.DataTableExtensions.CopyToDataTable(System.Collections.Generic.IEnumerable)'
cannot be inferred from the usage. Try
specifying the type arguments
explicitly
My code is:
DL.FVRGDataContext db = new FVRGDataContext();
public DataTable getRestaurants(string cuisineName)
{
var cuisineIdFind = from CUISINE in db.CUISINEs
where CUISINE.CUISINE_NAME == cuisineName
select CUISINE.CUISINE_ID;
var restaurantList = from RESTAURANT in db.RESTAURANTs
where RESTAURANT.CUISINE_ID == 2
orderby RESTAURANT.REST_NAME ascending
select i;
DataTable result = new DataTable();
result = restaurantList.CopyToDataTable();
return result;
}
CopyToDataTable doesn't work this way... it has a generic parameter T, where T must be a subclass of DataRow. In other words CopyToDataTable can't be used to convert an arbitrary collection to DataTable, the items of the collection must be DataRows themselves.
In your case, CUISINE and RESTAURANT seem to be Linq to SQL or Entity Framework entities, not DataRows, so it can't work.
I am very new to linq to sql and I am not sure how to actually delete a record.
So I been looking at this tutorial
http://weblogs.asp.net/scottgu/archive/2007/05/19/using-linq-to-sql-part-1.aspx
So for Update they have
NorthwindDataContext db = new NorthwindDataContext();
Product product = db.Products.Single(p => p.ProductName == "Toy 1");
product.UnitPrice == 99;
product.UnitsInStock = 5;
db.SubmitChanges();
For delete they have
NorthwindDataContext db = new NorthwindDataContext();
var toyProducts = from p in db.Producsts
where p.ProductName.Contains("Toy")
select p;
db.Products.RemoveAll(toyProducts);
db.SubmitChanges();
So do I have to query every time, to get the record in order to delete that record? Like I can sort of see doing this with update since you need to give it a record which to update first and then make the changes so I understand the querying part but not with delete.
Like can't you just send in what you want to delete and it goes and deletes it? why do you have to first get it and then tell it to be deleted?
Is that not 2 hits on the database?
Also I have foreign key relationship that I am trying to get to work. So I have this
public ViewResult(string param1, string param2)
{
Table A = new Table A
A.Field1 = param1;
A.Field2 = param2;
Delete(A);
}
private void Delete(Table A)
{
DbContext.A.DeleteAllOnsubmit(A.TableB);
DbContext.A.DeleteAllOnSubmit(A.TableC);
DbContext.A.DeleteOnSubmit(A);
}
So this fails it comes up with this message "Cannot remove an entity that has not been attached."
So I can see why the first 2 lines would fail in the delete method, since I made a new object and their is nothing in the object that has any information about TableB and TableC.
I however can't see why the last line still fails even if the 2 other lines where not there.
Like how I thought it would work it would take my Table A class object that I passed in and look through the table for that information contained in it. It does not seem to be the case though.
So do I first have to take the information out and then do a query to get it and then delete it, like in the example?
Also what is the difference between removeAll() and say DeleteAllOnSubmit().
Like I said I am new to linq to sql and have not been able to sit down and read a book on it due to time constraints. Once I have more time I will read through a book probably.
Thanks
You have several questions in your one question, but I will start with the simplest, about attaching, if you already have the primary key. If you don't have the primary key then I have always just done a fetch then a delete, but, whenever I do a fetch I tend to store the primary key for updates and deletes.
It will delete off of the primary key, but if you have that then just attach as I do below and call delete. I don't pass around the object needed by DLINQ as I want to be able to change it if I want, so I pass in a different User object and just pull the PK from the business class and put it into the DAO class.
var db = new MeatRequestDataContext();
if (input.UserID > 0)
{
entity = new User()
{
UserID = input.UserID
};
db.Users.Attach(entity);
db.Users.DeleteOnSubmit(entity);
}
this is a simple way to delete row from table by linq query.may be it helps .
var summary_delete = database.summeries.Find(id);
var delete = database.summeries.Remove(summary_delete);
database.SaveChanges();
reference : http://mvc4asp.blogspot.in/2013/09/how-to-delete-table-row-in-sql-database.html
Inserted_LINQDataContext db = new Inserted_LINQDataContext();
Item itm = new Item();
int ID = Convert.ToInt32(TextBox1.Text);
var DeleteID = from d in db.Items
where d.id == ID
select d;
db.Items.DeleteAllOnSubmit(DeleteID);
db.SubmitChanges();
Label2.Text = "Record deleted Successfully.";
TextBox1.Text = "";
where Item is Table name, Linserted_LINQDataContext is your Linq DB name, id is the Column name in Item table. Items is the alias name of Item table in linq.
SupportDataDataContext Retrive = new SupportDataDataContext();
// SupportDataDataContext delete = new SupportDataDataContext();
Topic res = Retrive.GetTable<Topic>().Single(t => t.ID == topicID);
if (res != null)
{
Retrive.Topics.DeleteOnSubmit(res);
Retrive.SubmitChanges(ConflictMode.ContinueOnConflict);
}
I know the question is old but this may be useful to someone:
"YourDataContext" dc = new "yourDataContext";
"YourTable" element = dc."YourTable".First(a => a.Id == 12345);
dc."YourTable".DeleteOnSubmit(element);
dc.SubmitChanges();