Is there any way of getting discriminated associations to work in Entity Framework 4? That is, where we have the following tables
TableA
RelatedEntityTypeId
RelatedEntityTypeKey
TableB (1)
Id
TableC (2)
Id
TableD (3)
Id
and I want to have three associations on the entity for TableA:
TableB
TableC
TableD
which are defined by the RelatedEntityTypeId and RelatedEntityTypeKey fields...when RelatedEntityTypeId = 1, then the association is to EntityB, when RelatedEntityTypeId = 2, then the association is to EntityC, etc.
Thanks.
I don't know your purpose of doing this. I have used following approach to solve similer problem.
You can define a base type for all three tables (A,B,C). And when you want retrieve a object use a generic method for all tables (which returns a base object). And then you can check the type of the returned object to get the A,B,C object.
TableBase
Id
TableB (1):TableBase
TableC (2):TableBase
TableD (3):TableBase
Related
i have below 3 tables
Table A: Table B: Table C:
id TableA id(foreign key) id
type TableC id(foreign key) name
i have requirement where i have to fetch everything from tableA but when i fetch i have to fetch the name associated from Table C based on the mapping from TableB.
it's a oneToOne mapping. i tried adding Embeddable , joincolumn but nothing works.
i was referring this link - https://vladmihalcea.com/the-best-way-to-map-a-many-to-many-association-with-extra-columns-when-using-jpa-and-hibernate/ and implemented same but still no luck.
how would i achieve this through spring boot JPA?
Can somebody help me on this?
I am trying to join two tables by a foreign key table in linq.
The two tables are
Items and Classes, and the foreign key table is ItemClasses (ItemId, ClassId).
My context does not have a DBSet for the foreign key table, and when I try to add it I get a model creation error.
When I saw the error, I noticed that this code referred to the foreign key table
modelBuilder.Entity<Classes>()
.HasMany(e => e.Items)
.WithMany(e => e.Classes)
.Map(m => m.ToTable("ItemClasses").MapLeftKey("ClassId").MapRightKey("ItemId"));
So it looks like I should be able to refer to the items through the class, but how do I join the tables?
I'd like to do something like this
query = from ig in myCtx.Items.AsNoTracking()
//join di in myCtx.ItemClasses.AsNoTracking() on ig.Id equals di.ClassId
join c in myCtx.Classes.AsNoTracking() on di.ClassId equals c.Id
join dd in myCtx.SalesAssociates.AsNoTracking() on dd.Id equals ig.SalesAssociateId
How do I do joins when the fk table is not in my context, but is referred to in one of the tables?
First, you have a configuration error. With HasMany / WithMany you are actually configuring the automatic "link" table, so
m.ToTable("Classes")
should be
m.ToTable("ItemClasses")
or how exactly you want that table to be named in the database.
Second, when working with EF, it's always preferred to use navigation properties rather than joins. In case of many-to-many relationship with auto link table, using navigation properties is mandatory. EF will produce the necessary joins for you.
So instead of join your would use something like this:
query = from ig in myCtx.Items.AsNoTracking()
from c in ig.Classes
...
I have an EF 4 data model with TPT mapping.
I have a strange behaviour about the generated SQL of a query .
Lets say entity A is a base entity , A has two derived entities B and C , also A has many associations with other entities (say E,D).
When I make a simple select on A , Context.A.First() , I profiled the generated SQL from this entity and it has all the joins with the other entities.
Do you have a ny suggestion why this happen ? fixes ? any tip.
Thanks in advance ...
Context.A is the set of all A entities - including all B and C entities because every B and C is an A. It is not the set of all A entities that are not a B or C.
Therefore, if you request the first A in the database by Context.A.First() it could be a B or C or just an A. To find the concrete type of that first A the only way with TPT inheritance is to check if there are related records in the B or C table that have the same primary key like the first record in the A table. If there are related records this A is of type B (or C) and all column values from the record in table B (or C) have to be loaded together with the column values from the base record in table A in order to materialize an entity object of the correct type B (or C). If there are no related records in table B or C the concrete type is just an A.
In any case a join to the related B or C tables is required to figure out if there is a record or not and to determine the concrete type of the first A.
So, the joins you are seeing are expected behaviour when you use TPT inheritance and you can't avoid them. It has a negative impact on performance, yes, which is the biggest downside of TPT modeling.
i need to map some parent children relationship on top of a legacy database, the problem is how the tables are structured.
tableA
id
name
tableB
id
tableA_parentId
tableA_childId
As showed I have two foreign key from tableA to tableB
Is there a way to map this relationship with EF i'm using the code first approach and have a configuration class per table
I need to get the 3rd level entities using navigation properties.
table1
table2
table3
table4
table5
Table 1 relates to table2 and table 2 relates to table 3,4,5 with foreign key relation ships.
I want to pull the data from table 3,4,5 based on the table1 fields. I tried to use the include method but unable to find the method. If you can give the sample code that would be very helpful.
Use the include method in System.Data.Objects. Include should work with the .Include("Table1.PropertyNameTable2.PropertyNameTable3.PropertyNameTable4"); notation.
http://msdn.microsoft.com/en-us/library/bb738708.aspx