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
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 have a legacy database with a particular table -- I will call it ItemTable -- that can have billions of rows of data. To overcome database restrictions, we have decided to split the table into "silos" whenever the number of rows reaches 100,000,000. So, ItemTable will exist, then a procedure will run in the middle of the night to check the number of rows. If numberOfRows is > 100,000,000 then silo1_ItemTable will be created. Any Items added to the database from now on will be added to silo1_ItemTable (until it grows to big, then silo2_ItemTable will exist...)
ItemTable and silo1_ItemTable can be mapped to the same Item entity because the table structures are identical, but I am not sure how to set this mapping up at runtime, or how to specify the table name for my queries. All inserts should be added to the latest siloX_ItemTable, and all Reads should be from a specified siloX_ItemTable.
I have a separate siloTracker table that will give me the table name to insert/read the data from, but I am not sure how I can use this with entity framework...
Thoughts?
You could try to use the Entity Inheritance to get this. So you have a base class which has all the fields mapped to ItemTable and then you have descendant classes that inherit from ItemTable entity and is mapped to the silo tables in the db. Every time you create a new silo you create a new entity mapped to that silo table.
[Table("ItemTable")]
public class Item
{
//All the fields in the table goes here
}
[Table("silo1_ItemTable")]
public class Silo1Item : Item
{
}
[Table("silo2_ItemTable")]
public class Silo2Item : Item
{
}
You can find more information on this here
Other option is to create a view that creates a union of all those table and map your entity to that view.
As mentioned in my comment, to solve this problem I am using the SQLQuery method that is exposed by DBSet. Since all my item tables have the exact same schema, I can use the SQLQuery to define my own query and I can pass in the name of the table to the query. Tested on my system and it is working well.
See this link for an explanation of running raw queries with entity framework:
EF raw query documentation
If anyone has a better way to solve my question, please leave a comment.
[UPDATE]
I agree that stored procedures are also a great option, but for some reason my management is very resistant to make any changes to our database. It is easier for me (and our customers) to put the sql in code and acknowledge the fact that there is raw sql. At least I can hide it from the other layers rather easily.
[/UPDATE]
Possible solution for this problem may be using context initialization with DbCompiledModel param:
var builder = new DbModelBuilder(DbModelBuilderVersion.V6_0);
builder.Configurations.Add(new EntityTypeConfiguration<EntityName>());
builder.Entity<EntityName>().ToTable("TableNameDefinedInRuntime");
var dynamicContext = new MyDbContext(builder.Build(context.Database.Connection).Compile());
For some reason in EF6 it fails on second table request, but mapping inside context looks correct on the moment of execution.
Considering this database:
This is what EF generates:
I think that HeroesItem class, is useless, and there should be a navigation property Items on Hero class and a navigation property Heroes on Item class.
I saw this can be done easily with code first, but how to get it done using database first?
It can be done only if your HeroesItems table does not contain Id column and instead uses IdHero and IdItem as composite primary key. Once you add any additional column to junction table you must map it as entity to have control over that column.
When we have two entities in EFv4 EDM diagram and only one table for both in the database (for instance, having table Documents and entities Invoice and Qoute), table Documents having documentTypeId column as a discriminator and set this column as a discriminator in the EDM (in Table mappings), how do we read the value of this property in our code?
We cannot assign values to it because EF does it for us under the hood (based on what we entered in Table mappings for condition) but somehow I don't get it why we are also not allowed to read it.
Imo this property is already mapped so you can't map it again. It is used to determine type of materialized entity. Why do you need such column. Usually it is enough to use is operator like:
var document = context.Documents.GetById(id);
if (document is Invoice)
{
...
}
If you only need to select subtypes you can use OfType extension method like:
var invoices = context.Documents.OfType<Invoice>().ToList();
You also don't need to set this value when adding new entity because you are adding subtype - Invoice or Quote.
Edit:
As I understand from your comment you don't need this information in query. In such case you don't need to map it. Simply use partial class of your entity and add custom property which will return your string. Sound like stupid solution but actually it would be the easiest one.
Discriminator column should be part of mapping metadata so in case of T4 template generating your entities, it could be possible to update the template so it generate such property for you.
You may want to use a single-table inheritance hierarchy, as described here.
That way, you could have an abstract Document class that includes a DocumentTypeId column. Invoices and Quotes would extend this class, but specify certain DocumentTypeId filters. However, because the original class has a DocumentTypeId column, they would each have that column as well.
Another advantage to this approach is that you could create utility methods that can act on any Document, and you could pass any Invoice or Quote to these methods.