I have a table called PCRStatusLog with a column called PromoteDate. This column is fed a date where data from an excel sheet was sent from staging to the primary database. It's a new column, hasn't been used yet so for most records it is null, but we need to display the data of this column to our webapp. Most of the logic to do so already exists and the models are ADO.NET entity models generated from EF Designer From Data Base in Visual Studio.
In the table, PromoteDate is DATETIME and nullable (SQL Server) and the model for the table looks like this:
public partial class PCRStatusLog
{
// ... list of fields and properties
public Nullable<System.DateTime> PromoteDate { get; set; }
}
And was generated code, not entered manually. There's nothing special about that class, it's only a list of getters/setters that map to a table, a typical simple entity model.
Here is where it is used (I didn't write most of this code, I only added changes concerning the PromoteDate):
public List<PCRTracking> GetPCRTrackingDetails()
{
//...
List<PCRTracking> pcrDetails = (from bulk in providerMasterContext.BULK_UPLOADS
join ps in providerMasterContext.PROCESSSTATUS on bulk.ProcessStatusID equals ps.ProcessStatusID
join p in providerMasterContext.PLANs on bulk.PlanCode equals p.PlanCode
where bulk.CreateDate > compDateTime
orderby bulk.BulkUploadID descending
select new PCRTracking
{
FileID = bulk.BulkUploadID,
FileName = bulk.BulkUploadActualFileName,
PlanName = p.PlanCode,
FileStatus = string.Empty,
RecordsSubmitted = 0,
RecordsFailed = 0,
ValidationStatusReports = string.Empty,
ErrorMessage = string.Empty,
Submitter = bulk.SubmissionByID,
SubmitterName = bulk.SubmissionByName,
SubmitDate = (DateTime)bulk.SubmissionDateTime
}).ToList<PCRTracking>();
foreach (PCRTracking item in pcrDetails)
{
var promoteDateQuery = (from psl in providerMasterContext.PCRStatusLogs
where psl.BulkUploadID == item.FileID
select psl).FirstOrDefault();
item.PromoteDate = promoteDateQuery.PromoteDate;
//... rest of the code doesn't make use of PromoteDate
All of the other fields in PCRTracking object work fine, but PromoteDate keeps coming up as null, even on the one record that I manually edited to have a date.
Even here, where I examine the object returned by querying the one record I know has a date under promote date, it turns out null:
// from the Main method of a test console project
var providerMasterContext = new BulkPCRDAL().providerMasterContext;
var query =(from psl in providerMasterContext.PCRStatusLogs
where psl.BulkUploadID == 43
select psl).FirstOrDefault();
foreach(var prop in query.GetType().GetProperties())
{
Console.WriteLine(prop.GetValue(query));
}
Console.ReadLine();
It grabs all the properties on the object, and everything looks right, and matches whats in the database, except this one PromoteDate property.
Am I missing something?
Note that everything else in this model works, all other fields display data from the db, this one field is the only one that won't work.
So I have a table called groupe_stg it contains 2 foreign keys code_demande , code_stagiaire and at the same time they are primary keys.
In my app I have the code_stagiaire and from it I want to retrieve it's code_demande. Basically what am trying to say is:
select code_demande
from group_stg
where code_stagiaire = "parameter"`
I would've create a stored procedure it would be easier , but unfortunately I was forced to work with an access database
This is my solution for the LINQ code,
String code_linq()
{
var query = from g in Program.mds.group_stg
where g.cin_stagiaire == txt_cin.Text
select new
{
code = g.code_demande
};
return query.ToString();
}
As you can see it is some sort a scalar function
but this code is giving me this exception:
system.data.enumerablerowcollection'1 [<>
f_anonymousType0'1[System.String]]
You are selecting multiple code_demande in an anonymous type but you want a single string.
If you just want the first code_demande which has cin_stagiaire == txt_cin.Text:
var demands = from g in Program.mds.group_stg
where g.cin_stagiaire == txt_cin.Text
select g.code_demande;
return demands.FirstOrdefault(); // null if no match
I know it's not something unusual to make such kind of queries but I think I get lost so I seek help. I have to tables with relation 1:N and to make it more clear I'll post a print screen from the management studio :
I am working on a asp.net mvc 3 project and I need to make a view where all Documents will be shown (and some filter and stuff, but I think that is irrelevant for this case). I need the data from the table Documents and only one specific record for each document from the DocumentFields table. This record is the record holding the name of the Document and it's uniqueness is DocumentID == Docmuents.Id, DocumentFields.RowNo == 1 and DocumentsFields.ColumnNo == 2. This is unique record for every Document and I need to get the FieldValue from this record which actually holds the Name of the Document.
I am not very sure how to build my query (maybe using JOIN) and I also would like to make my view strongly typed passing a model of type Documents but I'm not sure if it's possible, but I think depending on the way the query is build will determine the type of the model for the view.
I believe what you want is something like this:
var results =
from d in dbContext.Documents
join df in dbContext.DocumentFields
on new { d.Id, RowNo = 1, ColumnNo = 2 } equals
new { Id = df.DocumentId, df.RowNo, df.ColumnNo }
select new
{
Document = d,
DocumentName = df.FieldValue
};
Of course if you set up navigation properties, you can just do this:
var results =
from d in dbContext.Documents
let df = d.DocumentFields.First(x => x.RowNo == 1 && x.ColumnNo == 2)
select new
{
Document = d,
DocumentName = df.FieldValue
};
I´m having a problem, I retrieve all the Loans I have stored in my database like this:
list_loans = db.Loan.Where(x => x.State.id_state != 6).ToList();
db is the Object context.
Then, I assign that list as the DataSource for my DataGridView.
dgv_Loans.Datasource = list_loans;
With that info, I add some columns. Like for example, installments left to pay. I get that value by counting the result of a query.
The user can order the result using some options. Is easy to order the result from the fields that the entity have (using linq), but I dont know how to order the results using this new columns.
I read some posts here and tried this:
dgv_Loans.Sort(dgv_Loans.Columns["installments_left"], ListSortDirection.Ascending);
By doing this, I´m getting the following exception at runtime:
"DataGridView control must be bound to an IBindingList object to be sorted."
Is there anyway to use linq to orderby created columns in a DataGridViewColumn? Or how can I solve this error?
I know there are related posts, but after reading them, I can´t find a solution to this specific problem. Thats why I showed how I implemented to get some advice..
Rather than binding directly to the list retrieved from database, what I generally do is have a view class and have all the calculated properties in that class
public class LoanView : Loan {
public LoanView(Loan loan){
}
public int InsallmentsLeft { get { return ...; } }
}
and then bind the datasource to a list of this, this keeps sorting working.
Concerning about Sort datagridview by created columns using Entity Framework
I guess you need this Presenting the SortableBindingList<T>
Usage:
loanBindingSource.DataSource = new SortableBindingList<Loan>(list_loans.ToList());
dgv_Loans.Datasource = loanBindingSource;
int ID = Convert.ToInt32(cmbDepartments.SelectedValue);
var EmployeeList = from Employee in db.Employee
where Employee.DepartmentID == ID
select new
{
Employee.FirstName,
Employee.LastName
};
dataGridView1.DataSource = EmployeeList.ToList();
You could directly give the data source to dataGridView1.DataSource but you must write ToList() at the end of your query:
int ID = Convert.ToInt32(cmbDepartmanlar.SelectedValue);
dataGridView1.DataSource = (from Employee in db.Employee
where Employee.DepartmentID == ID
select new
{
Employee.FirstName,
Employee.LastName
}).ToList();
Lets say I query the database and load a list of items. Then I open one of the items in a detail view form, and instead of re-querying the item out of the database, I create an instance of the item from the datasource in the list.
Is there a way I can update the database record without fetching the record of the individual item?
Here is a sample how I am doing it now:
dataItem itemToUpdate = (from t in dataEntity.items
where t.id == id
select t).FirstOrDefault();
Then after pulling the record I update some values in the item and push the record back:
itemToUpdate.itemstatus = newStatus;
dataEntity.SaveChanges();
I would think there would be a better way to do this, any ideas?
You should use the Attach() method.
Attaching and Detaching Objects
You can also use direct SQL against the database using the context of the datastore. Example:
dataEntity.ExecuteStoreCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = 123 ");
For performance reasons, you may want to pass in variables instead of a single hard coded SQL string. This will allow SQL Server to cache the query and reuse with parameters. Example:
dataEntity.ExecuteStoreCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = {0}", new object[] { 123 });
UPDATE - for EF 6.0
dataEntity.Database.ExecuteSqlCommand
("UPDATE items SET itemstatus = 'some status' WHERE id = {0}", new object[] { 123 });
The code:
ExampleEntity exampleEntity = dbcontext.ExampleEntities.Attach(new ExampleEntity { Id = 1 });
exampleEntity.ExampleProperty = "abc";
dbcontext.Entry<ExampleEntity>(exampleEntity).Property(ee => ee.ExampleProperty).IsModified = true;
dbcontext.Configuration.ValidateOnSaveEnabled = false;
dbcontext.SaveChanges();
The result TSQL:
exec sp_executesql N'UPDATE [dbo].[ExampleEntities]
SET [ExampleProperty ] = #0
WHERE ([Id] = #1)
',N'#0 nvarchar(32),#1 bigint',#0='abc',#1=1
Note:
The "IsModified = true" line, is needed because when you create the new ExampleEntity object (only with the Id property populated) all the other properties has their default values (0, null, etc). If you want to update the DB with a "default value", the change will not be detected by entity framework, and then DB will not be updated.
In example:
exampleEntity.ExampleProperty = null;
will not work without the line "IsModified = true", because the property ExampleProperty, is already null when you created the empty ExampleEntity object, you needs to say to EF that this column must be updated, and this is the purpose of this line.
If the DataItem has fields EF will pre-validate (like non-nullable fields), we'll have to disable that validation for this context:
DataItem itemToUpdate = new DataItem { Id = id, Itemstatus = newStatus };
dataEntity.Entry(itemToUpdate).Property(x => x.Itemstatus).IsModified = true;
dataEntity.Configuration.ValidateOnSaveEnabled = false;
dataEntity.SaveChanges();
//dataEntity.Configuration.ValidateOnSaveEnabled = true;
Otherwise we can try satisfy the pre-validation and still only update the single column:
DataItem itemToUpdate = new DataItem
{
Id = id,
Itemstatus = newStatus,
NonNullableColumn = "this value is disregarded - the db original will remain"
};
dataEntity.Entry(itemToUpdate).Property(x => x.Itemstatus).IsModified = true;
dataEntity.SaveChanges();
Assuming dataEntity is a System.Data.Entity.DbContext
You can verify the query generated by adding this to the DbContext:
/*dataEntity.*/Database.Log = m => System.Diagnostics.Debug.Write(m);
Now native support for this in EF Core 7 — ExecuteUpdate:
Finally! After a long wait, EF Core 7.0 now has a natively supported way to run UPDATE (and also DELETE) statements while also allowing you to use arbitrary LINQ queries (.Where(u => ...)), without having to first retrieve the relevant entities from the database: The new built-in method called ExecuteUpdate — see "What's new in EF Core 7.0?".
ExecuteUpdate is precisely meant for these kinds of scenarios, it can operate on any IQueryable instance, and lets you update specific columns on any number of rows, while always issuing a single UPDATE statement behind the scenes, making it as efficient as possible.
Usage:
Imagine you wanted to update the Email column of a specific user:
dbContext.Users
.Where(u => u.Id == someId)
.ExecuteUpdate(b =>
b.SetProperty(u => u.Email, "NewEmail#gmail.com")
);
As you can see, calling ExecuteUpdate requires you to make calls to the SetProperty method, to specify which property to update, and also what new value to assign to it.
EF Core will translate this into the following UPDATE statement:
UPDATE [u]
SET [u].[Email] = "NewEmail#gmail.com"
FROM [Users] AS [u]
WHERE [u].[Id] = someId
Also, ExecuteDelete for deleting rows:
There's also a counterpart to ExecuteUpdate called ExecuteDelete, which, as the name implies, can be used to delete a single or multiple rows at once without having to first fetch them.
Usage:
// Delete all users that haven't been active in 2022:
dbContext.Users
.Where(u => u.LastActiveAt.Year < 2022)
.ExecuteDelete();
Similar to ExecuteUpdate, ExecuteDelete will generate DELETE SQL statements behind the scenes — in this case, the following one:
DELETE FROM [u]
FROM [Users] AS [u]
WHERE DATEPART(year, [u].[LastActiveAt]) < 2022
Other notes:
Keep in mind that both ExecuteUpdate and ExecuteDelete are "terminating", meaning that the update/delete operation will take place as soon as you call the method. You're not supposed to call dbContext.SaveChanges() afterwards.
If you're curious about the SetProperty method, and you're confused as to why ExectueUpdate doesn't instead receive a member initialization expression (e.g. .ExecuteUpdate(new User { Email = "..." }), then refer to this comment (and the surrounding ones) on the GitHub issue for this feature.
Furthermore, if you're curious about the rationale behind the naming, and why the prefix Execute was picked (there were also other candidates), refer to this comment, and the preceding (rather long) conversation.
Both methods also have async equivalents, named ExecuteUpdateAsync, and ExecuteDeleteAsync respectively.
I recommend using Entity Framework Plus
Updating using Entity Framework Core can be very slow if you need to update hundreds or thousands of entities with the same expression. Entities are first loaded in the context before being updated which is very bad for the performance and then, they are updated one by one which makes the update operation even worse.
EF+ Batch Update updates multiple rows using an expression in a single database roundtrip and without loading entities in the context.
// using Z.EntityFramework.Plus; // Don't forget to include this.
// UPDATE all users inactive for 2 years
var date = DateTime.Now.AddYears(-2);
ctx.Users.Where(x => x.LastLoginDate < date)
.Update(x => new User() { IsSoftDeleted = 1 });
Simple and elegant extension method:
I've written an extension method for DbContext that does exactly what the OP asked for.
In addition to that, it only requires you to provide a member initialization expression (e.g. new User { ... }), and it then figures out on its own what properties you've changed, so you won't have to specify them by hand:
public static void UpdateEntity<TEntity>(
this DbContext context,
int id,
Expression<Func<TEntity>> updateExpression
) where TEntity : BaseEntity, new()
{
if (updateExpression.Body is not MemberInitExpression memberInitExpr)
throw new ArgumentException("The update expression should be a member initialization.");
TEntity entityToUpdate = updateExpression.Compile().Invoke();
entityToUpdate.Id = id;
context.Attach(entityToUpdate);
var updatedPropNames = memberInitExpr.Bindings.Select(b => b.Member.Name);
foreach (string propName in updatedPropNames)
context.Entry(entityToUpdate).Property(propName).IsModified = true;
}
You also need a BaseEntity class or interface that has your primary key in it, like:
public abstract class BaseEntity
{
public int Id { get; set; }
}
Usage:
Here's how you'd use the method:
dbContext.UpdateEntity(1234 /* <- this is the ID */, () => new User
{
Name = "New Name",
Email = "TheNewEmail#gmail.con",
});
dbContext.SaveChanges();
Nice and simple! :D
And here's the resulting SQL that gets generated by Entity Framework:
UPDATE [Users]
SET [Name] = #p0, [Email] = #p1
WHERE [Id] = #p2;
Limitation:
This method only allows you to update a single row using its primary key.
So, it doesn't work with .Where(...), IQueryable<...>, and so on. If you don't have the PK, or you want to bulk-update, then this wouldn't be your best option. In general, if you have more complex update operations, then I'd recommend you use Entity Framework Plus, or similar libraries.
It works somewhat different in EF Core:
There may be a faster way to do this in EF Core, but the following ensures an UPDATE without having to do a SELECT (tested with EF Core 2 and JET on the .NET Framework 4.6.2):
Ensure your model does not have IsRequired properties
Then use the following template (in VB.NET):
Using dbContext = new MyContext()
Dim bewegung = dbContext.MyTable.Attach(New MyTable())
bewegung.Entity.myKey = someKey
bewegung.Entity.myOtherField = "1"
dbContext.Entry(bewegung.Entity).State = EntityState.Modified
dbContext.Update(bewegung.Entity)
Dim BewegungenDescription = (From tp In dbContext.Model.GetEntityTypes() Where tp.ClrType.Name = "MyTable" Select tp).First()
For Each p In (From prop In BewegungenDescription.GetProperties() Select prop)
Dim pp = dbContext.Entry(bewegung.Entity).Property(p.Name)
pp.IsModified = False
Next
dbContext.Entry(bewegung.Entity).Property(Function(row) row.myOtherField).IsModified = True
dbContext.SaveChanges()
End Using
ef core 7 :
public async Task<int> Update(UpdateLevelVm vm)
{
return await _db.Levels.Where(l => l.Id == vm.LevelId)
.ExecuteUpdateAsync(u => u
.SetProperty(l => l.GradeId, vm.GradeId)
.SetProperty(l => l.Title, vm.Title)
);
}
this has worked for me in EF core 3.1
await _unitOfWork.Context.Database.ExecuteSqlRawAsync("UPDATE Student SET Age = 22 Where StudentId = 123");
Generally speaking, if you used Entity Framework to query all the items, and you saved the entity object, you can update the individual items in the entity object and call SaveChanges() when you are finished. For example:
var items = dataEntity.Include("items").items;
// For each one you want to change:
items.First(item => item.id == theIdYouWant).itemstatus = newStatus;
// After all changes:
dataEntity.SaveChanges();
The retrieval of the one item you want should not generate a new query.