I have a table named product having product id, product bill id and.. the bill id is passed to my controller as a parameter.
I can use the entities from framework and find all rows with product id using
db.tbl_product.Find(product id).
But now i need to find all transactions using bill id. How do I do that??
Assuming tbl_product is a DbSet<Product> or something similar, you should be able to use LINQ to query the DbSet. To find a single item with a specific BillId property value, you would do something like this:
var product = db.tbl_product.FirstOrDefault(p => p.BillId == billId);
If there were multiple products with the same BillId, you could do the following:
var products = db.tbl_product.Where(p => p.BillId == billId);
It largely depends on the schema of the table and how you're using Entity Framework. I would highly recommend reading a book or tutorial on Entity Framework. There are lots of them out there, for example: Entity Framework Tutorial.
Related
I am new to EF so please bear with me. I am using Entity Framework with an existing database in which the relationships are not defined.
Using EF, I am able to produce the model, but obviously the 'navigational properties' are not working. Is there a way I can specify the mapping between the entities?
For example, in my Product entity, I have a field CategoryID_fk (maps to Category entity). But since the relationships are not defined, I cannot load a Category while loading a Product entity.
Can someone guide me in this regard?
I do understand that it would be preferable to refactor our database but I am unable to do that now. Thanks in advance.
This link is very useful.http://www.entityframeworktutorial.net/
I think field names are not suitable conventions.Try to change field name as CategoryId or Category_CategoryId .I think it will work
Yes, you can do a group join. Basically you will retrieve Products and Category in separate queries and take an approach as indicated in this answer.
Something along these lines:
var productCategoryList = products.GroupJoin
(
categories,
p=> p.productId,
c=> c.CategoryId,
(p, c) => new ProductCategory
{
//Create your Product Category model here
}
).AsEnumerable();
Is it possible to include a computed field in an EF entity? Example, lets say I have a shop selling products, and the products are grouped into categories.
When the list of categories is displayed for editing to the administrator of the shop I wish to list the number of products in each category as part of the list.
In NHibernate I would use a formula e.g.
<property name="Products" formula="dbo.Category_NumProducts(id)" />
I can't work out if something similar is possible for EF. I know I could make a category view and map this to a second entity but that seems wrong as its almost a complete duplication.
EDIT: If this isn't possible in EF, then what is the best way to accomplish this?
Unfortunately if your Category table doesn't have this as computed column you will not be able to map it without creating second entity - it leads to database view, defining query in EDMX or perhaps Query view in EDMX (but Query view may not work because you require aggregate function to be computed).
Edit:
IMHO the simplest solution (and also the best) is simply creating a ViewModel (some non mapped class) and use projection in Linq query:
var query = from c in context.Categories
where ...
select new CategoryView {
Id = c.Id,
Name = c.Name,
...
Products = c.Products.Count()
};
i'm struggling with LLBLGEN and i guess ORM's in general.
i have created an entity, lets use a library example to explain:
i want to display a book object and also return a list of users who have loaned the book.
so i need to return the book object which contains a list of users.
DTO Book::
int bookId,
string bookName
additionally i wish to return with my book a collection of users who have loaned the book:
List<user> Loans
loans table might look like this:
int id
int userid
int bookid
currently my loans entity has now created this:
DTO Loans
int id
User user // user entity
Book book // book entity
im struggling to understand how this example would work in llblgen. can anyone assist with guidance or point me in the way of a tutorial?
at the moment, when i come up to update my model Book with a new loan associated to a book, im getting stackoverflow errors. i assume this is creating some sort of loop when attempting to update my Book object.
thanks
i noticed when running a profiler on SQL that the sql statement didnt include any join statements onto my relationship entities.
this was because my domain query didnt include prefetch items for my relationships, i added the following to my query:
var query = new DomainSearch<T>
{
SearchText = searchText,
PrefetchItems =
{
new Prefetch(typeof(Users))
}
};
To make sure, you are looking for a list of User entities that have loaned a particular Book entity. Is this the correct use case, or are you looking for a list of User entities that have borrowed the particular book?
Regardless, LLBLGen's support for these cases is great with referencing relationships between entities and using related entities quickly and easily.
Presuming you're looking up a book by unique BookId/ISBN/etc....
// Get the specific book entity
BookEntity book = new BookEntity(bookId);
foreach(UserEntity user in book.users)
{
// do stuff with list of users
}
It's just that simple assuming you've defined your relationships between entities.
Suppose I have
table Person
table Employee, which inherits Person.
I want to get a list of Person, regardless if this Person is Employee or not. How do you get entity framework to do that without joining the Employee table? C# is what I'm using. Thanks.
You need to make sure that you don't implicitly use any information from Employee.
If you do this:
var people = Context.People.ToList();
... Then me Entity Framework will initialize new instances of type Employee for those people who happen to be employees. This is because when you store an Employee in the database, you generally expect to get an Employee back when you select the same item.
Nor, for that matter, can you tell the Entity Framework to give you a Person when the stored value is an Employee. The Entity Framework will never give you back an incorrect entity type.
However, if you do just want to read the one table, there is a way to do that: Select the data from Person into a non-entity types, such as an anonymous type:
var people = Context.People.Select(p => new { Name = p.Name }).ToList();
i've got a database with a table named PropertyValues where i store every value i need to describe some properties of my database table rows.
For example, table Products which looks like this :
ID
OrderID //Products table is related with Order table
ProductName
ProductType_ID // ID of PropertyValues table which describes product type (food, parfume, chemicals)
ProductCountry_ID // ID of PropertyValues table which links to country where product came from
ProductStatusID //also ID of PropertyValues table which contains product status(availible, not availible)
with such database model, to get order and all it's products with their type, country and status i'll have to write something like this :
var orders = from o in dbEntities.Order.Include("Products.ProductType")
.Include("Products.ProductCountry")
.Include("Products.ProductStatus")
select o;
and the question is :)
can it be done automatically ( so all related entities will be included )
or maybe there is better approach ?
Thank You !
I think what you are looking for is either "Lazy Loading" or "Eager Loading" as Alex James pointed out.
This blog post explains that "Lazy Loading" is to be implemented in version 4.0 of the Entity Framework.
http://blogs.msdn.com/adonet/archive/2009/05/12/sneak-preview-deferred-loading-in-entity-framework-4-0.aspx
It can be done automatically, Google "Entity Framework lazy loading" to go about setting it up.