I want to know if there is way to create a database out of existing classes with the ado.net entity framework or to map existing classes to a database.
I looked for tutorials and only found ways to create the classes with the entity model designer.
As an example I have the class Bird with Properties Length and Age
On the database I have a table named Bird with columns Length and Age
Now I don't want the designer to create new classes out of the database. Instead I want to map the Class Bird directly to the table Bird. With Linq2Sql this was possible by creating the mapping manually. Is there a possibility in the ado.net entity framework?
With kind regards
Sebastian
What's the difference between mapping a class C onto a table T or mapping T onto a class C ?
O/R mapping isn't about mapping classes to tables, it's about defining an entity model and projecting it to tables AND classes simultaneously. After all, your classes and tables don't fall out of the sky: they're based on definitions you have, e.g. there has to be an entity customer, with fields A, B and C, and THEN you're defining the entity Customer with fields A, B and C which leads to a table Customer with fields A, B and C and a class Customer with fields / properties A, B and C and the mapping between them, because they represent the same entity
Related
I have a table and a view which share the same columns and I'm trying to add them to EDM. I created an abstract entity type and 2 derived types A and B.
Initially I tried creating 2 entity sets, one for each of the derived types, and proceeded to add the EntitySetMapping (using IsTypeOf per MS MSL specifications for EntityTypeMapping of derived type) but got an error in the .edmx file that each of the types doesn't have an entity set and isn't mapped.
To solve this, I created a single EntitySet with type as the base EntityType (the abstract one) and used 2 EntityTypeMapping children tags, specifying the StoreEntitySet as the table or the view accordingly. This resolved the issue but created a single DbSet<BaseType> and now I cannot retrieve data from the view or the table using DbContext.
Any ideas on how to properly solve this?
Thanks
I am trying to implement a number of base/sub classes using Entity Framework, database first. Following some online tutorials, I have decided to attempt TPT inheritance.
On the database, I have a base class table 'Location', and two sub class tables: 'StreetAddress' and 'RuralRouteAddress'. I have defined a foreign key constraint between the sub class tables and the base class table on their primary keys. 'Location's Primary Key is an auto-increment column, and the two sub class tables' primary keys are not auto-increment.
In Entity Framework, I defined the 'Base Type' of the two sub classes as 'Location'. I then deleted the associations (and their corresponding navigation properties) from the model. I also deleted the ID column mappings from the sub classes, as ID is now inherited from the 'Location' base class.
This seems to have worked. I haven't tried updating/inserting, but querying returns the data with proper inheritance in place.
My problem is that, whenever I 'Update Model from Database', he inheritance association lines stay, but the FK associations between the base class and the sub classes are brought back... . I then have to delete them, and realign the association lines on my diagram (I'm a bit picky about the layout of the model diagram).
This isn't so bad, but the project that I would like to use TPT inheritance in has a lot of inheritance. Having to delete a ton of associations and reorganize my entire diagram every time I update the model is not very appealing.
Did I do something wrong when I implemented inheritance? Is there a way to ignore/exclude certain associations from being created when updating the model?
The relationships you define in the database will always reappear when you update the model from the database. This is by design. If you want to have classes in the model that have a different relationship structure, try creating a complex model from a stored procedure that selects all the columns (or all the columns you want) from the base table. Import that procedure and in the Function Imports, edit the return type by creating a new complex type, or even just renaming the result that EF automatically creates. Then add your associations on that type, and use it as the base type for your inherited classes.
The good part of this is that you can adjust the type structure to match any table changes by editing the stored procedure, then using "Get Column Information" and "Update" to bring the complex type into line. It won't overwrite your associations because they aren't defined in the database, but it is almost as straightforward as using TPT.
Joey
I'm facing two problems by trying to make a model first or code first using TPH concept.
The problem is that I need to use table per hierarchy at three levels, so that:
When I use Model First, the last hierarchy entity (third level) does not saves in database. I create an instance from this entity which inherits an abstract entity, which inherits another abstract entity. The data of two abstract entities are saved, but the last entity not saves. If the inheritance goes at maximum two levels works fine.
If I try to use Code First the problem is that I cannot share attributes with same name, for example: ClassB and ClassC has a property named "Name", and both inherits ClassA. When I map to generate database, I want to create only a sql table called ClassA, but it does not share the column "Name", it creates Name and Name1 columns.
I need to do one of this models works, otherwise I can't use inheritances in my model.
Hope some help!
Thanks
I have very big table in my Database and a can't modify it.
So i have BaseEntity type for table.
I have several children (entity1, entity2) and i'd like to map each type to same column ("Date") and name properties differently.
Surely i can't move all same column properties to base type cause there is about 100 columns in my super table (it's not my design i've jst need to map it)
So i have 0019 error and is there any way to solve it or EF not for me?
No. TPH requires that each property defined in derived entity is exclusive for that entity (no other entity can map to the same column). This targets more general rule in EF - each column can be mapped only once. So if you need to use some column in more entities it must be defined in parent and must have same name in all child entities.
Lets say I have 2 tables on my physical model, Receipt(ID, Location) and LineItem(ID, ReceiptID, ItemName) where a Receipt has multiple LineItems and ReceiptID is a Foreign Key to Receipt's ID.
I want to model these as a single table in my conceptual model, where I only see a table of LineItems with the Location included on each LineItem.
Every time I try to model this in the Entity Modeler, I get an error about how the Primary Key must be the same for every table being combined into the single conceptual entity.
Is this even possible to model using the entity framework?
Thanks!
No there is no way to model this directly. You must either create database view and map that view or import both entities and create QueryView in the model. In both cases resulting entity combining your two tables will become readonly and the only way to support CUD operations will be mapping stored procedures.