I am new in EF Core (5), and read about the separation of concerns, so, as I understood, for EF there is need to put attributes (like, readonly, ColumnName, table name, etc) on the model entites...
Is there a way to configure all these attributes on json config or something like this in order do not mess the SQL Data information and the business model classes?
Say, I would like to create a class User but in the DB the table name would be Utilisateurs
Related
In my database I have
a Members table which contains basic member details (MemberId [primary key - auto generated number], MemberName, IsActive).
a MembersDetails table which contains more detailed information about the member (Address, Phone, Birthday ...). MembersDetails has MemberId field as a foreign key to the Members table.
There's a reason (part of the app logic) that the 2 tables are separated and are not all in one table.
I've created a view that gets a full member details (a join of the 2 tables), and Entity Framework created an object that represents the view.
I have 2 questions:
Is there a better way of flattening 2 joined tables into an object other than creating a view in the database?
I would like to create an object of the view type (a full user details), initialize it's properties and insert it to the database (which will put the info it needs in the Members table, the the generated id, and than insert to the MemberDetails table). Is there a way to do that?
Ad 1.
I think a database view will be a good choice for performance reasons.
But you can investigate an inheritance provided with the Entity Framework.
It allows you join two separated tables in one model object containing all properties (from "derived" and "base" table). Note, it will be OK for one to one relations (but not for one to many).
Implementing Inheritance with the Entity Framework 6 in an ASP.NET MVC 5 Application
Ad 2.
The Entity Framework inheritance will help you with this issue well. Alternatively, if you can use a database view, just create stored procedures for inserting and updating data included in a view, then map the stored procedures for specified actions on the view model generated by Entity Framework.
I have used the Entity Data Model Wizard to generate an EF data model (an edmx with POCO's) based on the Object Catalogue Views in SQL Server, i.e. sys.objects, sys.tables, sys.columns, etc. When I try to access any data through my DbContext's DbSet properties, EF throws a ModelValidationException, complaining that entities don't have keys defined.
I can easily modify the T4 template that generates the entity POCOs to include a dummy property marked with the [Key] attribute, but this seems a bit klunky, as now my entity classes have a 'phantom' property that doesn't belong to them. Choosing a name for the key column is also an issue, but I could do something like generate a GUID for a unique key column name for ever class.
But, isn't there a better, neater way of telling EF I don't need key columns, as this model is strictly read only?
ADDENDUM: If I use the Entity Framework Power Tools - Reverse Engineer Code First tool, it creates a mapping class (derived from EntityTypeConfiguration) for each entity, and where the entity has no define key, it defines one using all the fields in the entity.
I am trying to create a custom Entity Framework (4.2) entity that would be mapped to my database like it would be done in a Code first approach.
The issue is that my entity framework data model is using Database first.
How can I add my custom entity to entity framework's context?
If by the Database first you mean that you already have EDMX created from exiting database you simply cannot use code first. You must create table and update model (EDMX) from the database to include it in EDMX.
Edit based on comment:
I want to create a BriefUser entity that would basically be a lighter
version of User but it would have properties retrieved from User's
foreign keys.
Well this is possible. You can either create BriefUser as common class and use projection in query.
var breifUser = (from x in context.Users
where ...
select new BriefUser
{
// Fill BreifUser's properties here
}).FirstOrDefault();
You can even refactor former code to reusable extension method:
public static IQueryable<BriefUser> ProjectUser(this IQueryable<User> query)
{
return query.Select(x => new BreifUser()
{ // Fill BreifUser's properties here });
}
and use it like:
var briefUser = context.Users.ProjectUser().FirstOrDefault(...);
It is also possible to define your new class as "entity view". The first problem is that each table can be mapped to only one entity (except some advanced concepts like inheritance or splitting) so you cannot define your BriefUser as a new entity type because mapping both User and BriefUser to UserTbl would violate this rule. You must use special construct called QueryView.
QueryView is view in mapping level. It allows you to create new mapped type which is projection of existing mapped entities defined directly in EDMX's MSL part. The projection is defined as custom Entity SQL query. The problem is that QueryView has limitations:
It doesn't offer all Entity SQL features - for example it doesn't support aggregations (which I consider as really missing feature). Without aggregations you for example cannot create a new type which will contain property counting some related entities.
It is not supported in designer. You must edit your EDMX as XML to define QueryView and you must write Entity SQL query yourselves.
Resulting type is a "view" and it is read-only.
I want to keep the EDMX file, but also be able to add an entity
(BriefUser) to EF's context.
This is not possible. Your BreifUser is only projection / view and EF is not able to track changes back to originating tables so you cannot add BreifUser to context and persist it. In case of QueryView you can achieve it if you define custom stored procedures which will no how to decompose BreifUser and modify all related tables. These stored procedures must be imported to the EDMX and mapped to data modification operations of the view entity. Btw. same will happen if you map your entity to the database view because EF takes all views as read-only.
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.
We've started using Entity Framework 4 for data access and have come across an issue or perhaps lack of understanding.
Our current system is heavily reliant on Stored Procedures, these procedure contain some necessary business logic so we need to continue to use these when doing Select/Insert/Update/Delete.
The issue we are having is the following:
We've mapped a table to an entity, let's say for example this is a User entity and has the following properties - UserId, FirstName, LastName
Now in our sproc to insert a user we accept FirstName, LastName, CreatedById as parameters.
As our User Entity has no CreatedById we get an error indicating that no property of our Entity can be mapped to the "CreatedById" parameter.
Now one thing we've tried is to manually add a CreatedById scalar property to our Entity, but this results in the issue that there is no Field in our User table in the data source that maps to CreatedById. In general the additional property that we'd like to pass in is not something that is stored.
Now there is potential solution to this in that we can just map the procedures to Function Imports and not bother with using the .AddObject, .DeleteObject, .SaveChanges way of manipulating our objects but that doesn't feel like the way to go about it.
that's a good question. There are few options i can tell u.
instead of mapping the entity to the table, map it a view and have the view return CreatedById and then your problem would be solved.
Second option is to create overloaded stored procedure that takes only FirstName, LastName and calls the actual stored procedure with a default value for CreatedById. You can create overloads at the database layer or create it in the model in the ssdl layer which supports inline stored procedure.
exec myproc #firstName,#LastName,null