I have a data model as follows:
A Customer has Products and Payment Methods. Each Product can be assigned any or all of the Customer's Payment Methods, with one set as default.
Foreign Keys are:
Customer.CustomerId => Product.CustomerId
Customer.CustomerId => PaymentMethod.CustomerId
Product.ProductId => ProductPaymentMethod.ProductId
PaymentMethod.PaymentMethodId => ProductPaymentMethod.PaymentMethodId
I want to customise this model for presentation purposes, Customer to have a collection of Payment Methods and a collection of Products. Products to have a collection of ProductPaymentMethods which inherit from PaymentMethod.
I deleted the association between PaymentMethod and ProductPaymentMethod, added an inheritence from PaymentMethod to ProductPaymentMethod and deleted PaymentMethodId from ProductPaymentMethod.
This is now my model:
When I save the model or build the project I get 2 errors:
Error 3002: Problem in mapping
fragments starting at line
226:Potential runtime violation of
table ProductPaymentMethod's keys
(ProductPaymentMethod.ProductPaymentMethodId):
Columns
(ProductPaymentMethod.ProductPaymentMethodId)
are mapped to EntitySet
PaymentMethods's properties
(PaymentMethods.ProductPaymentMethodId)
on the conceptual side but they do not
form the EntitySet's key properties
(PaymentMethods.PaymentMethodId).
and
Error 3003: Problem in mapping
fragments starting at line 226:All the
key properties
(PaymentMethods.PaymentMethodId) of
the EntitySet PaymentMethods must be
mapped to all the key properties
(ProductPaymentMethod.ProductPaymentMethodId)
of table ProductPaymentMethod.
What am I doing wrong?
EDIT: Having done some further Googling, I have found several solutions, most of which don't quite fit this scenario. Most talk about inheritance requiring a 1-1 not 1-many relationship. However, because of the Customer to Product 1-many relationship, the model requires a 1-many between PaymentMethod and ProfilePaymentMethod. Is it not possible to do what I am attempting?
My only answer to this so far is to have some manually created POCO classes for presentation and a Mapper class to turn my data entity into a presentation entity
Related
I'm having trouble configuring entity relationships when one entity inherits from another. I'm new to ADO Entity Framework -- perhaps someone more experienced has some tips for how this is best done. I'm using .net 4.
Database tables with fields:
Products (int ID, nvarchar Description)
FoodProducts (int ProductID, bit IsHuge)
Flavors (int ID, int FoodProductID, nvarchar Description)
There are constraints between Products and FoodProducts as well as FoodProducts and Flavors.
Using the designer I create a model from the database. The designer seems to get it right, with a 1:0..1 association between Product and FoodProduct entities, and 1:* association between Flavor and FoodProduct. No errors when I save or build.
Next I set FoodProduct entity to inherit from Product entity. Then I get errors concerning relationship between Product and FoodProduct. Ok, starting fresh, I first delete the relationship between Product and FoodProduct before setting the inheritance. But now I get errors about the relationship between FoodProduct and Flavor. So I delete and then recreate that relationship, connecting Flavor.ID to FoodProduct.ProductID. Now I get other errors.
My question is this: Should I instead be creating relationship between Flavor.FoodProductID and Product.ID? If so, I assume I then could (or should) delete the FoodProduct.ProductID property. Since my database will have many of these types of relationships, am I better off first creating the entity model and exporting the tables to SQL, or importing the database schema and then making many tweaks?
My intent is that there will be several types of products, some of which require many additional fields, some of which do not. So there may be zero or one FoodProducts records associated with each Product record. At least by my thinking, the table for each sub-type (FoodProducts) should be able to "borrow" the primary key from Products (as a FK) to uniquely identify each of its records.
You can find a screen capture here: http://img218.imageshack.us/img218/9720/entityframework.jpg (I'd embed the img but haven't earned the requisite rep' yet!)
Well, I deleted the FoodProduct.ProductID field, as it should always return the same value as Product.ID anyway. Then, as you hinted, I had to manually map the Products.ID field to FoodProducts.ProductID field. Errors resolved. I'll write a little code to test functionality. Thanks for the "observations"!
Couple of observations:
FoodProducts needs a primary key (e,g identity - FoodProductID). Are you sure it should be a 1:0..1 between Food and FoodProducts? I would have thought it should be 1:0..*. For this cardinality to work you need a unique PK on this table.
When you setup inheritance for entities, the parent entity's properties are inherited. So FoodProducts will inherit ID from the Product table.
BUT, on the physical model (database), this field still needs to be mapped to a column on the FoodProducts table - which is why you need the identity field.
After you setup inheritance, you still need to map all the columns on the derived tables. My money is on you have not mapped "ID" on FoodProducts to any column.
If you screencapped your model and show the errors you are getting it would be much easier to diagnose the issue.
Please help an EF n00b design his database.
I have several companies that produce several products, so there's a many-to-many relationship between companies and products. I have an intermediate table, Company_Product, that relates them.
Each company/product combination has a unique SKU. For example Acme widgets have SKU 123, but Omega widgets have SKU 456. I added the SKU as a field in the Company_Product intermediate table.
EF generated a model with a 1:* relationship between the company and Company_Product tables, and a 1:* relationship between the product and Company_Product tables. I really want a : relationship between company and product. But, most importantly, there's no way to access the SKU directly from the model.
Do I need to put the SKU in its own table and write a join, or is there a better way?
I just tested this in a new VS2010 project (EFv4) to be sure, and here's what I found:
When your associative table in the middle (Company_Product) has ONLY the 2 foreign keys to the other tables (CompanyID and ProductID), then adding all 3 tables to the designer ends up modeling the many to many relationship. It doesn't even generate a class for the Company_Product table. Each Company has a Products collection, and each Product has a Companies collection.
However, if your associative table (Company_Product) has other fields (such as SKU, it's own Primary Key, or other descriptive fields like dates, descriptions, etc), then the EF modeler will create a separate class, and it does what you've already seen.
Having the class in the middle with 1:* relationships out to Company and Product is not a bad thing, and you can still get the data you want with some easy queries.
// Get all products for Company with ID = 1
var q =
from compProd in context.Company_Product
where compProd.CompanyID == 1
select compProd.Product;
True, it's not as easy to just navigate the relationships of the model, when you already have your entity objects loaded, for instance, but that's what a data layer is for. Encapsulate the queries that get the data you want. If you really want to get rid of that middle Company_Product class, and have the many-to-many directly represented in the class model, then you'll have to strip down the Company_Product table to contain only the 2 foreign keys, and get rid of the SKU.
Actually, I shouldn't say you HAVE to do that...you might be able to do some edits in the designer and set it up this way anyway. I'll give it a try and report back.
UPDATE
Keeping the SKU in the Company_Product table (meaning my EF model had 3 classes, not 2; it created the Company_Payload class, with a 1:* to the other 2 tables), I tried to add an association directly between Company and Product. The steps I followed were:
Right click on the Company class in the designer
Add > Association
Set "End" on the left to be Company (it should be already)
Set "End" on the right to Product
Change both multiplicities to "* (Many)"
The navigation properties should be named "Products" and "Companies"
Hit OK.
Right Click on the association in the model > click "Table Mapping"
Under "Add a table or view" select "Company_Product"
Map Company -> ID (on left) to CompanyID (on right)
Map Product -> ID (on left) to ProductID (on right)
But, it doesn't work. It gives this error:
Error 3025: Problem in mapping fragments starting at line 175:Must specify mapping for all key properties (Company_Product.SKU) of table Company_Product.
So that particular association is invalid, because it uses Company_Product as the table, but doesn't map the SKU field to anything.
Also, while I was researching this, I came across this "Best Practice" tidbit from the book Entity Framework 4.0 Recipies (note that for an association table with extra fields, besides to 2 FKs, they refer to the extra fields as the "payload". In your case, SKU is the payload in Company_Product).
Best Practice
Unfortunately, a project
that starts out with several,
payload-free, many-to-many
relationships often ends up with
several, payload-rich, many-to-many
relationships. Refactoring a model,
especially late in the development
cycle, to accommodate payloads in the
many-to-many relationships can be
tedious. Not only are additional
entities introduced, but the queries
and navigation patterns through the
relationships change as well. Some
developers argue that every
many-to-many relationship should start
off with some payload, typically a
synthetic key, so the inevitable
addition of more payload has
significantly less impact on the
project.
So here's the best practice.
If you have a payload-free,
many-to-many relationship and you
think there is some chance that it may
change over time to include a payload,
start with an extra identity column in
the link table. When you import the
tables into your model, you will get
two one-to-many relationships, which
means the code you write and the model
you have will be ready for any number
of additional payload columns that
come along as the project matures. The
cost of an additional integer identity
column is usually a pretty small price
to pay to keep the model more
flexible.
(From Chapter 2. Entity Data Modeling Fundamentals, 2.4. Modeling a Many-to-Many Relationship with a Payload)
Sounds like good advice. Especially since you already have a payload (SKU).
I would just like to add the following to Samuel's answer:
If you want to directly query from one side of a many-to-many relationship (with payload) to the other, you can use the following code (using the same example):
Company c = context.Companies.First();
IQueryable<Product> products = c.Company_Products.Select(cp => cp.Product);
The products variable would then be all Product records associated with the Company c record. If you would like to include the SKU for each of the products, you could use an anonymous class like so:
var productsWithSKU = c.Company_Products.Select(cp => new {
ProductID = cp.Product.ID,
Name = cp.Product.Name,
Price = cp.Product.Price,
SKU = cp.SKU
});
foreach (var
You can encapsulate the first query in a read-only property for simplicity like so:
public partial class Company
{
public property IQueryable<Product> Products
{
get { return Company_Products.Select(cp => cp.Product); }
}
}
You can't do that with the query that includes the SKU because you can't return anonymous types. You would have to have a definite class, which would typically be done by either adding a non-mapped property to the Product class or creating another class that inherits from Product that would add an SKU property. If you use an inherited class though, you will not be able to make changes to it and have it managed by EF - it would only be useful for display purposes.
Cheers. :)
I'm sure I'm missing something very simple, but let's say I have two entities, Employee and EmployeeType.
Employee type would contain values like 'Full time', 'Contractor', 'Intern', etc.
An Employee entity would contain one, and only one EmployeeType value.
So I am designing a new .edmx model using the Model-First approach and generating my actual sql server data schema from the model.
I want to add an integer type foreign key id into my Employee entity, EmployeeTypeId, which will map to the primary key of the EmployeeType entity.
So I've gone ahead and done that in my Employee entity. Where I'm stuck is how, though the Entity Framework designer, to enforce the 1:1 referential constraint on that EmployeeTypeId property? Or does the EF handle that automatically behind the scenes?
thanks in advance,
John
Think I figured out the answer to my own question. In the EF .edmx surface designer, I needed to right click on the scalar property I wanted to set as a foreign key id to the other entity and choose 'Entity Key'.
Once that was done, I could go into the referential constraints dialog box and point my new foreign key property to the other entity.
If you don't explicitly set your foreign key property as 'Entity Key', EF will think you want to point your primary key id to the other table.
cheers
You first create a new association (if you haven't done this already) between the two entities. Just right-click on the edmx designer and choose Add -> Association.
When you click on the association you have just created in the model designer, in the properties window, you can set the End1 Multiplicity and End2 Multiplicity properties to 1. This will ensure that you can set only one relation entity while using the entity framework. This does not get enforced in SQL server by the way, because SQL server does not implicitly support 1:1 relationships.
I have a table [User] and another table [Salesperson] in my database. [Salesperson] defines a unique UserID which maps to [User].UserID with a foreign key. When I generate the model with Entity Framework I get a 1-to-Many relationship between [User]-[Salesperson], meaning that each User has a "Collection of Salesperson", but what I want is a 0..1-to-1 relationship where each User has a nullable reference to a "Salesperson".
I tried fiddling around with the XML and changing the association's multiplicity settings, but that only produced build errors. What I am trying to achieve is no different than having a nullable SalespersonID in [User] that references [Salesperson].SalespersonID, but because salespeople only exist for specific users it feels like I'd be muddying up my [User] table structure just to get the relationship to point the right way in Entity Framework.
Is there anything I can do to change the multiplicity of the relationship?
Make the PK of Salesperson itself a FK to User. The EF's GUI designer will then get the cardinality correct, since PKs are unique.
I am using the Entity Framework with SQL Server. I have a many to many relationship between 2 tables. I have created a join table with just the primary key fields of the 2 tables. In the designer, the 2 tables now have a navigation property to the other with return types of Collection of X where X is the other entity. So far, everything just as it should be. The setup looks correct.
Task TaskProducts Product
========== ============ =======
TaskID TaskID ProductID
Description ProductID Name
Not every task will have a product or products associated with it. What do I assign to the Products navigation property of the Task table when there is no associated Product for that Task?
Do I build up a EntityCollection collection with the Product entities and assign that to the Products navigation property on the Task entity when I do have Product entities?
When doing updates(adding, removing and changing) to the Products navigation property on the Task entity, do I work with it like any other collection? Are there any special things to look out for?
I would be interested in any help working with many to many relationships in the Entity Framework.
Edit(11/17/2009)
One thing I learned is that to a many to many relationship work with a join table, BOTH fields in the join table need to be marked as primary keys;
MSDN has good documentation on managing many-to-many relationships in the Entity Framework:
http://msdn.microsoft.com/en-us/library/bb738695.aspx
The prescriptive guidance for inserts is to call the "Add" method on the entity collection and specify the related object (versus setting the Value property on the entity reference for a one-to-many relationship.)
Updates are handled just like any other EF update... load the desired object, set the changed properties and call SaveChanges on the context.
Deletes are handled the same as well, call DeleteObject on the context and then SaveChanges.