How can I apply changes to the first record in a table and add one or more additional records to the same table? I am getting the following exception:
An object with the same key already exists in the ObjectStateManager.
The ObjectStateManager cannot track multiple objects with the same key
See sample code below.
var Student = db.Student.Where(d => d.StudentID == studentID);
int count = 0;
if(Student != null)
{
foreach(var student in Student)
{
if (student.Id == id)
{
foreach (var assign in assignment)
{
if (assign != null && count == 0)
{
//How can I save the changes that is made to the first record here
assign.AssignmentId = student.AssignmentID;
db.Assignment.ApplyCurrentValues(assign);
}
if (assign != null && count > 0)
{
//How can I add new records here
assign.AssignmentId = student.AssignmentID;
db.Assignment.AddObject(assign);
}
count++;
}
}
}
}
Try calling save after this line i.e.
db.Assignment.ApplyCurrentValues(assign);
db.SaveChanges();
Then for your new entries:
var assignment = new Assignement() { AssignmentId = student.AssignmentID };
db.Assignments.Add(model);
db.SaveChanges();
Related
In my C# application i am using linq. I need a help what is the syntax for if-elseif- using linq in single line. Data, RangeDate are the inputs. Here is the code:
var Date1 = RangeData.ToList();
int record =0;
foreach (var tr in Date1)
{
int id =0;
if (tr.Item1 != null && tr.Item1.port != null)
{
id = tr.Item1.port.id;
}
else if (tr.Item2 != null && tr.Item2.port != null)
{
id = tr.Item2.port.id;
}
if (id >0)
{
if(Data.Trygetvalue(id, out cdat)
{
// Do some operation. (var cdata = SumData(id, tr.item2.port.Date)
record ++;
}
}
}
I think your code example is false, your record variable is initialized to 0 on each loop so increment it is useless .
I suppose that you want to count records in your list which have an id, you can achieve this with one single Count() :
var record = Date1.Count(o => (o.Item1?.port?.id ?? o.Item2?.port?.id) > 0);
You can use following code:
var count = RangeData.Select(x => new { Id = x.Item1?.port?.id ?? x.Item2?.port?.id ?? 0, Item = x })
.Count(x =>
{
int? cdate = null; // change int to your desired type over here
if (x.Id > 0 && Data.Trygetvalue(x.Id, out cdat))
{
// Do some operation. (var cdata = SumData(x.Id, x.Item.Item2.port.Date)
return true;
}
return false;
});
Edit:
#D Stanley is completely right, LINQ is wrong tool over here. You can refactor few bits of your code though:
var Date1 = RangeData.ToList();
int record =0;
foreach (var tr in Date1)
{
int? cdat = null; // change int to your desired type over here
int id = tr.Item1?.port?.id ?? tr.Item2?.port?.id ?? 0;
if (id >0 && Data.Trygetvalue(id, out cdat))
{
// Do some operation. (var cdata = SumData(id, tr.Item2.port.Date)
record ++;
}
}
Linq is not the right tool here. Linq is for converting or querying a collection. You are looping over a collection and "doing some operation". Depending on what that operation is, trying to shoehorn it into a Linq statement will be harder to understand to an outside reader, difficult to debug, and hard to maintain.
There is absolutely nothing wrong with the loop that you have. As you can tell from the other answers, it's difficult to wedge all of the information you have into a "single-line" statement just to use Linq.
I am using LINQtoSQL and I need to compare object before and after update.
In the example below Student 'before' and Student 'curStudent' are the same, because they was retrieved by the same query.
using(DataContext db = new DataContext())
{
Student before = db.Student.Where(q=>q.id == 1).SingleOrDefault();
Student curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before.Name != curStudent.Name) // this condition will never be true
{
//do something
}
The context will only keep one object per key value, so one way would be to use two separate contexts:
Student before;
using(DataContext db1 = new DataContext())
{
before = db.Student.Where(q=>q.id == 1).SingleOrDefault();
}
Student curStudent;
using(DataContext db2 = new DataContext())
{
curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before.Name != curStudent.Name)
{
//do something
}
Or if you're just interested in the name change, keep the previous value:
string before;
using(DataContext db = new DataContext())
{
Student curStudent = db.Student.Where(q=>q.id == 1).SingleOrDefault();
before = curStudent.Name; // cache the name
curStudent.Name = "NewName";
db.SubmitChanges();
}
if(before != curStudent.Name)
{
//do something
}
Im trying to write a method which will allow me to search different DataTables, over different columns.
So far i have the following:
string selectedValue;
string searchColumn;
string targetColumn;
var results = (from a in dt.AsEnumerable()
where a.Field<string>(searchColumn) == selectedValue
select new
{
targetColumn = a.Field<string>(targetColumn)
}).Distinct();
Which kind of gets the job done, but I'm left with the column name as targetColumn rather than the actual column name I want.
Is there any way to resolve this?
Thanks in advance
CM
I make a LINQ to Datatables
public List<DataRow> Where(this DataTable dt, Func<DataRow, bool> pred)
{
List<DataRow> res = new List<DataRow>();
try {
if (dt != null && dt.Rows.Count > 0) {
for (i = 0; i <= dt.Rows.Count - 1; i++) {
if (pred(dt(i))) {
res.Add(dt(i));
}
}
}
} catch (Exception ex) {
PromptMsg(ex);
}
return res;
}
Usage :
var RowsList = dt.Where(f => f("SomeField").toString() == "SomeValue" ||
f("OtherField") > 5);
I'm using Linq to return data from an XML file to a DataTable and that works. But now I'm trying to modify the code to loop through the DataTable. I created a custom class to model the data and have a List in my model. When I loop through the DataTable to display records it displays System.Collections.Generic.List`1[System.String] instead of the actual data. I'm not sure what to search to find the answer.
Snippet:
foreach (DataRow row in tbl.Rows)
{
myList = row["myList"] + ", " + myList;
}
The myList column is the List. I hope this makes sense.
Edited:
public static DataTable LINQToDataTable<T>(IEnumerable<T> varlist)
{
DataTable dtReturn = new DataTable();
// column names
PropertyInfo[] oProps = null;
if (varlist == null) return dtReturn;
foreach (T rec in varlist)
{
// Use reflection to get property names, to create table, Only first time, others will follow
if (oProps == null)
{
oProps = ((Type)rec.GetType()).GetProperties();
foreach (PropertyInfo pi in oProps)
{
Type colType = pi.PropertyType;
if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition() == typeof(Nullable<>)))
{
colType = colType.GetGenericArguments()[0];
}
dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
}
}
DataRow dr = dtReturn.NewRow();
foreach (PropertyInfo pi in oProps)
{
dr[pi.Name] = pi.GetValue(rec, null) == null ?DBNull.Value :pi.GetValue
(rec,null);
}
dtReturn.Rows.Add(dr);
}
return dtReturn;
}
hobbiesList = (List<string>)row["hobbies"];
foreach (var item in hobbiesList)
{
hobbies.Add(item.ToString());
}
hobby = string.Join(", ", hobbies.ToArray());
hobbies.Clear();
I had to do the above to get it to work. I then add hobby to my output array.
this is the way i used to save record with linq: (my Q is below)
public void SaveEmployee(Employee employee)
{
using (BizNetDB db = new BizNetDB())
{
BizNet.SqlRep.Data.Employee oldEmployee = (from e in db.Employees
where e.EmployeeID == employee.EmployeeID
select e).SingleOrDefault();
if (oldEmployee == null)
{
oldEmployee = new BizNet.SqlRep.Data.Employee();
oldEmployee.BirthDate = employee.BirthDate;
oldEmployee.WorkRole = employee.WorkRole;
oldEmployee.CurrentFlag = employee.CurrentFlag;
oldEmployee.HireDate = employee.HireDate;
...
db.Employees.InsertOnSubmit(oldEmployee);
}
else
{
if (oldEmployee.BirthDate.Date != employee.BirthDate.Date)
oldEmployee.BirthDate = employee.BirthDate;
if (oldEmployee.CurrentFlag != employee.CurrentFlag)
oldEmployee.CurrentFlag = employee.CurrentFlag;
if (oldEmployee.HireDate.Date != employee.HireDate.Date)
oldEmployee.HireDate = employee.HireDate;
}
oldEmployee.ModifiedDate = DateTime.Now;
db.SubmitChanges();
employee.EmployeeID = oldEmployee.EmployeeID;
}
}
my questions are:
a. are the if statements nesccery? why not to make the assigning without the
check?
mybe the if block take more cpu..
b. why to spearate the new record block and the update block?
when the record is new it will do
db.Employees.InsertOnSubmit(oldEmployee);
and then proceed with the update routine...
The way you're doing it the only reason you need the if statement is to new it up and insert it, so I would use the if statement just for that.
I would do this instead:
public void SaveEmployee(Employee employee)
{
using (BizNetDB db = new BizNetDB())
{
BizNet.SqlRep.Data.Employee oldEmployee =
(from e in db.Employees
where e.EmployeeID == employee.EmployeeID
select e).SingleOrDefault();
if (oldEmployee == null)
{
oldEmployee = new BizNet.SqlRep.Data.Employee();
db.Employees.InsertOnSubmit(oldEmployee);
}
if (oldEmployee.BirthDate.Date != employee.BirthDate.Date)
oldEmployee.BirthDate = employee.BirthDate;
if (oldEmployee.CurrentFlag != employee.CurrentFlag)
oldEmployee.CurrentFlag = employee.CurrentFlag;
if (oldEmployee.HireDate.Date != employee.HireDate.Date)
oldEmployee.HireDate = employee.HireDate;
oldEmployee.ModifiedDate = DateTime.Now;
db.SubmitChanges();
employee.EmployeeID = oldEmployee.EmployeeID;
}
}
I also think there's a way to map one object's properties to the other, but it escapes me at the moment. It may not work for what you're trying to do anyway since it seems that you're doing some other things later anyway with the ModifiedDate and EmployeeID.