I am trying to insert the data into 'Order' , 'OrderDetails' tables at the same time. How can I get Auto generated OrderID from the Order table. I am using ADO.NET Entity model.
Thanks..
Use this code:
var order = new Order();
//fill your properties here
var orderDetails = new OrderDetails();
//fill your properties here
orderDetails.Order = order;
db.AddToOrders(order);
db.AddToOrderDetails(orderDetails);
//Save changes
db.SaveChanges();
Hope it will help you with your problem.
Related
I'm using Entity Framework and I am trying to remove a NinjqEquiment from a list belonging to an instance of Ninja.When I retrieve the list of Ninjas,I make sure to include the equipment list, so I know they are there. Then I remove the equipment from the Ninja and try to save changes. I get the following error -
The entity type List`1 is not part of the model for the current
context.
using (var db = new NinjaDbContext())
{
//get ninjas with equipment included
var ninjas = GetAllNinjas();
//get ninja
var ninja = (from n in ninjas
where n.Id == id
select n).FirstOrDefault();
//get equipment
var eq = (from e in ninja.EquipmentOwned
where e.Id == removeEqId
select e).FirstOrDefault();
//remove eq from ninja
ninja.EquipmentOwned.Remove(eq);
//Make sure entity knows EquipmentOwned has been modified
db.Entry(ninja.EquipmentOwned).State = EntityState.Modified;
//save ninja
db.SaveChanges();
}
Just remove this:
//Make sure entity knows EquipmentOwned has been modified
db.Entry(ninja.EquipmentOwned).State = EntityState.Modified;
This causes the error.
EquipmentOwned is a List<Equipment>. It is not an Entry in EF terms so it is not tracked directly by it.
When you delete an entity from such collection, EF knows that there won't be any relationship between this particular ninja and this particular equipment. It won't delete equipment from database because other ninjas may use this equipment.
To delete it completely you should remove this equipment from corresponding DbSet<> like this:
using (var db = new NinjaContext())
{
//db.Equipment is a DbSet<Equipment>
//id is PrimaryKey of Equipment table
var eq = db.Equipment.Find(id);
db.Equipment.Remove(eq);
db.SaveChanges();
}
Morning,
I would like to know how to write the following SQL statement in LINQ.
SELECT TOP 6 * FROM Questions
ORDER BY NEWID()
I would also like to know, how i could bind this to a asp.net repeater control to display the 6 questions.
Many thanks :)
The Linq style would be
Questions.OrderBy(q=>Guid.NewGuid()).Take(6)
then you attach that to a repeater by setting its DataSource property to the above, and calling the DataBind method.
You would have to be able to invoke the NEWID() function to generate your random guids. To do so, you could take some hints here and first create a pseudo-method mapped to the NEWID() function on your data context.
[System.Data.Linq.Mapping.Function(Name="NEWID", IsComposable=true)]
public Guid NewId()
{
throw new NotImplementedException();
}
Once that is set, you could then write your query to use this function:
var query = dc.Questions
.OrderBy(question => dc.NewId())
.Take(6);
You can inspect the SQL query generated for this and it should match.
Questions.OrderBy(q=>Sql.NewGuid()).Take(6)
This will invoke the NEWID() in SQL statement.
(from db in context.Questions
order by Guid.NewGuid()
select db).Take(6);
I know answer is already selected, but still I'm adding my way to achieve this. Faced same situation today and tried couple of ways, used questions.OrderBy(q => Guid.NewGuid()).ToList() and couple of more suggestions. Later I thought to add a new field string RandomOrder in view model and assigned Guid.NewGuid().ToString() in loop and then used questions.OrderBy(i => i.RandomOrder).ToList() and this worked great.
I had requirement to shuffle questions if author selected option shuffleAlways while creating assessment. If not then sort on regular sorting order. Here is complete solution:
private List<AssessmentQuestionsViewModel> LoadAllQuestions(string assessmentId, bool shuffleQuestions)
{
List<AssessmentQuestionsViewModel> questions = new List<AssessmentQuestionsViewModel>();
var items = assessmentQuestionRepository.GetAll().Where(i => i.AssessmentId == assessmentId).ToList();
foreach (var item in items)
{
questions.Add(new AssessmentQuestionsViewModel
{
Id = item.Id,
AssessmentId = item.AssessmentId,
QuestionText = item.QuestionText,
HintText = item.HintText,
QuestionType = item.QuestionType,
MaxMarks = item.MaxMarks,
SortOrder = item.SortOrder,
RandomOrder = Guid.NewGuid().ToString(),
Answers = LoadAllAnswers(item.Id)
});
}
if (shuffleQuestions)
{
questions = questions.OrderBy(i => i.RandomOrder).ToList();
}
else
{
questions = questions.OrderBy(i => i.SortOrder).ToList();
}
return questions;
}
And this worked like charm. Hope this help others.
I assume you are using ORDER BY NEWID() as a way to select random data from your questions? If so, you should avoid using NEWID() (or it's LINQ equivalent), causes tons a new guid to be generated for every record in your table. On a large dataset, that's devestating.
Instead, see Linq Orderby random ThreadSafe for use in ASP.NET for an optimized solution to random sorts. Then just add a take operator and your set.
Random random = new Random();
int seed = random.Next();
var RandomQuestions = Questions.OrderBy( s => (~(s.Shuffle & seed)) & (s.Shuffle | seed)); // ^ seed);
return RandomQuestions.Take(6);
I am pretty new to Entity Framework. I am getting an error as
An object with a temporary EntityKey value cannot be attached to an
object context
I think I am doing something wrong.
I have a Customer table and Address table where the Address table has customer's ID as foreign key.
I want to add a new address to the customer entity and keep in session and in next call I want to save it. this is only an example.
using (var db = new MyModel())
{
Customer cust = db.Customers.SingleOrDefault(c => C.ID == 1);
Address addr = new Address();
addr.Street = "123 super st";
cust.Addresses.Add(addr);
Session["customer"] = cust;
}
Customer SessionCustomer = (Customer)Session["customer"];
Customer.Comments = "Added new address";
using (var db = new MyModel())
{
db.Customers.Attach(SessionCustomer); //This throws exception: An object with a temporary EntityKey value cannot be attached to an object context
db.ObjectStateManager.ChangeObjectState(SessionCustomer, System.Data.EntityState.Modified);
db.SaveChanges();
}
Any help is appreciated. thank you.
Try using db.Customers.AddObject() for reattaching object to datacontext.
Take also a look at this: http://msdn.microsoft.com/en-us/library/system.data.objects.objectcontext.addobject.aspx
Cheers
Linq to entity query to delete a specific column from a table by matching a condition`
public ActionResult deleteChecks(string checkValue)
{
check_master checks = (from table in db.check_master
where table.check_code == checkValue
select table).First();
//now how to delete/remove checks.mcheck
return View("Edit");
}`
Only want to update a single column element with null value(of selected row) from the table check_master
You can set a single property (which maps to a column) to null and save it to the database
foreach(check_master check in checks)
{
check.mcheck = null;
}
db.SaveChanges();
using (NorthwindDataContext db = new NorthwindDataContext())
{
// Retrieve the existing entity. Database Call 1
Product product = db.Products.First(p => p.ProductID == 1);
// Change the properties. LINQ to SQL knows
// these specific properties have changed.
product.UnitsInStock = 14;
// Flush the changes. Database Call 2
db.SubmitChanges();
}
Entity framework works with constant table scheme only.
Tell please, what your global aim is, may be there's some more suitable way to do it.
Updated:
foreach(var chm in db.check_master)
{
chm.mcheck = null;
}
db.SaveChanges();
I believe that Linq to Entities only support DML, it does not support DDL operations.
So you would have to use stored procedure or ADO.NET raw query.
EDIT
you can do simple update like this :
public ActionResult deleteChecks(string checkValue)
{
check_master checks = (from table in db.check_master
where table.check_code == checkValue
select table).First();
checks.mcheck = null;
db.SaveChanges();
return View("Edit");
}`
im using poco code first . how do i get the last insert after savechanges() ?
thanks
I resolve that problem in such way:
with Max() - you can get last id from table
db.Products.Add(product);
db.SaveChanges();
int lastProductId = db.Products.Max(item => item.ProductId);
ProductId is Key() and increment
register = db.registers.CreateObject();
register.id = 0;
register.customer = h.customer;
register.employee = employee_created;
register.created = DateTime.Now;
db.registers.AddObject(register);
db.SaveChanges();
//You can get the ID here
int last_insert_id = register.id;
After you've saved an entity in the context (SaveChanges()). The ID property on the poco itself should be set by the entity framework.
If you actually want more information about the modified entities, you can look for them in the ObjectStateManager provided by the Entity Framework's ObjectContext.
var newProduct = db.Product.Add(model);
db.SaveChanges();
var productId = model.Id;
It automatically adds it to the object you are saving
Refer to the following example -
db.Hotels.Add(hotels);
db.SaveChanges();
var id = hotels.Id;
It worked for me.
Source - https://dzone.com/articles/how-return-id-field-after