I have a DomainService which I am trying to delete records from.
Assuming the following rough code server-side method:
public IQueryable<Employee> GetAllEmployees()
{
DataLoadOptions loadOpts = new DataLoadOptions();
loadOpts.LoadWith<Models.Employee>(e => e.PhoneNumber);
this.DataContext.LoadOptions = loadOpts;
return this.DataContext.Employees;
}
This means that when I load all my employees, all their Phone Numbers are included.
I can do the following client side code, with phoneNumber being an entity:
domainContext.Employees.PhoneNumbers.Remove(phoneNumber);
This, as I understand it, removes the relationship between Employee and PhoneNumber entitities, but what I really want is the complete removal of PhoneNumber from the database. How can I accomplish this?
Assuming PhoneNumbers is also an Entity on the Client side, then you can do the following:
domainContext.Employees.PhoneNumbers.Remove(phoneNumber); // remove relationship
domainContext.PhoneNumbers.Remove(phoneNumber); // remove entity
Related
I have a GridView which needs to page and sort data which comes from a collection of Customer objects.
Unfortunately my customer information is stored separately...the customer information is stored as a Customer ID in my database, and the Customer Name in a separate DLL.
I retrieve the ID from the database using Entity Framework, and the name from the external DLL through a partial class.
I am getting the ID from my database as follows:
public class DAL
{
public IEnumberable<Customer> GetCustomers()
{
Entities entities = new Entities();
var customers = (from c in entities.Customers
select c);
//CustomerID is a field in the Customer table
return customers;
}
}
I have then created a partial class, which retrieves the data from the DLL:
public partial class Customer
{
private string name;
public string Name
{
if (name==null)
{
DLLManager manager = new DLLManager();
name= manager.GetName(CustomerID);
}
return name;
}
}
In my business layer I can then call something like:
public class BLL
{
public List<Customer> GetCustomers()
{
DAL customersDAL = new DAL();
var customers = customersDAL.GetCustomers();
return customers.ToList();
}
}
...and this gives me a collection of Customers with ID and Name.
My problem is that I wish to page and sort by Customer Name, which as we have seen, is populated from a DLL. This means I cannot page and sort in the database, which is my preferred solution. I am therefore assuming I am going to have to call of the database records into memory, and perform paging and sorting at this level.
My question is - what is the best way to page and sort an in-memory collection. Can I do this with my List in the BLL above? I assume the List would then need to be stored in Session.
I am interested in people's thoughts on the best way to page and sort a field that does not come from the database in an Entity Framework scenario.
Very grateful for any help!
Mart
p.s. This question is a development of this post here:
GridView sorting and paging Entity Framework with calculated field
The only difference here is that I am now using a partial class, and hopefully this post is a little clearer.
Yes, you can page and sort within you list in the BLL. As long as its fast enough I wouldn't care to much about caching something in the session. An other way would be to extend your database with the data from you DLL.
I posted this question slightly differently on a different forum, and got the following solution.
Basically I return the data as an IQueryable from the DAL which has already been forced to execute using ToList(). This means that I am running my sorting and paging against an object which consists of data from the DB and DLL. This also allows Scott's dynamic sorting to take place.
The BLL then performs OrderBy(), Skip() and Take() on the returned IQueryable and then returns this as a List to my GridView.
It works fine, but I am slightly bemused that we are perfoming IQueryable to List to IQueryable to List again.
1) Get the results from the database as an IQueryable:
public class DAL
{
public IQueryable<Customer> GetCustomers()
{
Entities entities = new Entities();
var customers = (from c in entities.Customers
select c);
//CustomerID is a field in the Customer table
return customers.ToList().AsQueryable();
}
}
2) Pull the results into my business layer:
public class BLL
{
public List<Customer> GetCustomers(intint startRowIndex, int maximumRows, string sortParameter)
{
DAL customersDAL = new DAL();
return customersDAL.GetCustomers().OrderBy(sortParameter).Skip(startRowIndex).Take(maximumRows).ToList();
}
}
Here is the link to the other thread.
http://forums.asp.net/p/1976270/5655727.aspx?Paging+and+sorting+Entity+Framework+on+a+field+from+Partial+Class
Hope this helps others!
I am retrieving data about books from lots of different sources such as XML and web services which I then store in the database using EF Code First 6 via a Generic Repository and and obviously DbContext.
The problem is that performance is very bad.
I have the following (fictional but analogous) POCO in my Model
public class Book
{
public int Id {get; set;}
public string Title {get; set;}
}
also
public class BookDataSource
{
public int Id {get; set;}
public virtual List<Book> Books {get; set;};
}
So I retrieve the book data from some source and construct the above book object.
I then need to check whether the book already exists in the DB and update it if it does or insert it if it does not. I also need to then delete any books that no longer exist on the data source.
//The following method takes the data source (type: IBookDataSource) to update from as the parameter
public string UpdateBooks(BookDatasource dataSource)
{
string successMessage = "";
//Disconnected entities
List<Book> retreivedBooks= dataSource.RetreiveBooks();
foreach (Book retreivedBook in retreivedBooks)
{
//Check if the dataSource already contains a book (based on title)
Book localBook =
dataSource.Books.SingleOrDefault(
b => b.Title== retreivedBook.Title);
if (localBook ==null)
{
//Insert a new one
_unitOfWork.BookRepository.Insert(retreivedBook);
}
else
{
//Update existing
localBook.Title= retreivedPortalMerchant.PortalsMerchantName;
_unitOfWork.PortalMerchantRepository.Update(localPortalMerchant);
}
}
//Soft delete any existing ones that no longer exist in the received data
foreach (Book existingBook in dataSource.Books)
{
if ( !retreivedBooks.Exists(
b => m.Title == existingBook.Title))
{
existingBook.Deleted = true;
_unitOfWork.PortalMerchantRepository.Update(existingBook);
}
}
}
However the performance is very bad. Sometimes there are 25000 books retrieved from the data source and I am having to do two for loops. ForEach retreived book, check if one exists in the db the insert/update accordingly. And another one to loop all existing books and check whether it no longer exists on the datasource and soft delete.
Is there a better way to attach the entities and monitor their state. In the above example I think I am querying the context each time and not the DB so why such bad performance. Should I revert to T-SQL?
For the proper algorithm of inserting-updating-deleting disconnected entities, you can check "Setting the State of Entities in a Graph" section of "Chapter 4. Working with Disconnected Entities Including N-Tier Applications" of "Programming Entity Framework: DbContext by Julia Lerman, Rowan Miller" book.
Also in this SO answer some ways to increase performance of EF is explained. The answer is for bulk inserting however it may work for your scenerio also.
The fastest way would be using bulk insert extension
Here's maxlego's description:
It uses SqlBulkCopy and custom datareader to get max performance. As a result it is over 20 times faster than using regular insert or AddRange EntityFramework.BulkInsert vs EF AddRange
context.BulkInsert(hugeAmountOfEntities);
I want to use EF DbContext/POCO entities in a detached manner, i.e. retrieve a hierarchy of entities from my business tier, make some changes, then send the entire hierarchy back to the business tier to persist back to the database. Each BLL call uses a different instance of the DbContext. To test this I wrote some code to simulate such an environment.
First I retrieve a Customer plus related Orders and OrderLines:-
Customer customer;
using (var context = new TestContext())
{
customer = context.Customers.Include("Orders.OrderLines").SingleOrDefault(o => o.Id == 1);
}
Next I add a new Order with two OrderLines:-
var newOrder = new Order { OrderDate = DateTime.Now, OrderDescription = "Test" };
newOrder.OrderLines.Add(new OrderLine { ProductName = "foo", Order = newOrder, OrderId = newOrder.Id });
newOrder.OrderLines.Add(new OrderLine { ProductName = "bar", Order = newOrder, OrderId = newOrder.Id });
customer.Orders.Add(newOrder);
newOrder.Customer = customer;
newOrder.CustomerId = customer.Id;
Finally I persist the changes (using a new context):-
using (var context = new TestContext())
{
context.Customers.Attach(customer);
context.SaveChanges();
}
I realise this last part is incomplete, as no doubt I'll need to change the state of the new entities before calling SaveChanges(). Do I Add or Attach the customer? Which entities states will I have to change?
Before I can get to this stage, running the above code throws an Exception:
An object with the same key already exists in the ObjectStateManager.
It seems to stem from not explicitly setting the ID of the two OrderLine entities, so both default to 0. I thought it was fine to do this as EF would handle things automatically. Am I doing something wrong?
Also, working in this "detached" manner, there seems to be an lot of work required to set up the relationships - I have to add the new order entity to the customer.Orders collection, set the new order's Customer property, and its CustomerId property. Is this the correct approach or is there a simpler way?
Would I be better off looking at self-tracking entities? I'd read somewhere that they are being deprecated, or at least being discouraged in favour of POCOs.
You basically have 2 options:
A) Optimistic.
You can proceed pretty close to the way you're proceeding now, and just attach everything as Modified and hope. The code you're looking for instead of .Attach() is:
context.Entry(customer).State = EntityState.Modified;
Definitely not intuitive. This weird looking call attaches the detached (or newly constructed by you) object, as Modified. Source: http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx
If you're unsure whether an object has been added or modified you can use the last segment's example:
context.Entry(customer).State = customer.Id == 0 ?
EntityState.Added :
EntityState.Modified;
You need to take these actions on all of the objects being added/modified, so if this object is complex and has other objects that need to be updated in the DB via FK relationships, you need to set their EntityState as well.
Depending on your scenario you can make these kinds of don't-care writes cheaper by using a different Context variation:
public class MyDb : DbContext
{
. . .
public static MyDb CheapWrites()
{
var db = new MyDb();
db.Configuration.AutoDetectChangesEnabled = false;
db.Configuration.ValidateOnSaveEnabled = false;
return db;
}
}
using(var db = MyDb.CheapWrites())
{
db.Entry(customer).State = customer.Id == 0 ?
EntityState.Added :
EntityState.Modified;
db.SaveChanges();
}
You're basically just disabling some extra calls EF makes on your behalf that you're ignoring the results of anyway.
B) Pessimistic. You can actually query the DB to verify the data hasn't changed/been added since you last picked it up, then update it if it's safe.
var existing = db.Customers.Find(customer.Id);
// Some logic here to decide whether updating is a good idea, like
// verifying selected values haven't changed, then
db.Entry(existing).CurrentValues.SetValues(customer);
I have an object that has been populated with the contents of four different related entities. However i have another entity in which i cannot include as part of the query due to it not being related in the navigation properites directly to the IQueryable table i am pulling. The entity i am trying to include is related to one of the four different entities that have been included successfully.
Is there a way to include(during db hit or afterwards) this entity as part of the overall object i am creating?
Here is an example of what my calls look like to build the CARTITEM object:
public List<CARTITEM> ListCartItem(Guid cartId)
{
//Create the Entity object
List<CARTITEM> itemInfo = null;
using (Entities webStoreContext = new Entities())
{
//Invoke the query
itemInfo = WebStoreDelegates.selectCartItems.Invoke(webStoreContext).ByCartID(cartId).ToList();
}
//Return the result set
return itemInfo;
}
here is the selectCartItems filter(Where i would normally do the includes):
public static Func<Entities, IQueryable<CARTITEM>> selectCartItems =
CompiledQuery.Compile<Entities, IQueryable<CARTITEM>>(
(cart) => from c in cart.CARTITEM.Include("ITEM").Include("SHIPPINGOPTION").Include("RELATEDITEM").Include("PROMOTION")
select c);
from this i have my CARTITEM object. Problem is i want to include the PROMOTIONTYPE table in this object, but since the CARTIEM entity doesn't have a navigation property directly to the PROMOTIONTYPE table i get an error.
Let me know if you need any more clarification.
Thanks,
Billy
You can use join and if it is the same database and server it should generate the join in SQL and do it all in one call...
LinqToEnties join example
I'm having problems querying the entity model to get additional information.
My db has a Program table with a one to many relation with an Events table. The Entity model generates the relationships just fine, but I'm unable to figure out how to query the model to get the progam object with its events.
I can do this:
var foo = from program in entities.ProgramSet
where program.StartDate > DateTime.now
orderby program.StartDate
select program;
No problems there. From what I've found on Microsofts Page (Shaping queries with Entity framework): msdn.microsoft.com/en-us/library/bb896272.aspx, if I wanted to get the child objects, I just do the following:
// Define a LINQ query with a path that returns
// orders and items for a contact.
var contacts = (from contact in context.Contact
.Include("SalesOrderHeader.SalesOrderDetail")
select contact).FirstOrDefault();
However, there is no .Include or Include that I can find on the query.
Any suggestion? I know that I can do a foreach across the results, then run a .Events.Load() on it, but doesn't that force the IQueriable result to execute the sql, instead of optomize it to run only when a .ToList() etc is called on it?
Here is some sample code from my project:
public class ProgramRepository : CT.Models.IProgramRepository
{
CTEntities db = new CTEntities();
public IQueryable<Program> FindAllPrograms()
{
return db.ProgramSet;
}
public IQueryable<Program> FindUpcomingPrograms()
{
var programs = from program in FindAllPrograms()
where program.StartDate > DateTime.Now
orderby program.StartDate
select program;
return programs;
}
With the FindUpComingPrograms I would like to have it also include the Events Data. There is a relationship between the Program and Events model. Program has a List<Events> property, that I would like to fill and return with the IQueryable method.
Thanks again!
The Include Function is part of the ObjectQuery object...
I think you are going to need to re-write your query to look something like this:
var contacts = context.Contact.Include("SalesOrderHeader.SalesOrderDetail").FirstOrDefault();
//Not sure on your dot path you might have to debug that a bit
Here is an Article that has some examples...