Relational: Entity splitting support

[divega]

This work item represents the mapping capability to slice the data contained by an object into multiple tables.

Limitations:

• Properties mapped to multiple columns can't use store-generated values
• Foreign keys and indexes split across tables won't be created in the database

Related: #17270 (comment)

[ilmax]

I would love if this feature does not fill in the standard Relational library but perhaps is exposed as a additional feature (pay for play scenario) which I can plug in only if needed

[AndriySvyryd]

Related to TPT #2266

[ajcvickers]

Note: consider optional relationships: #9773

[AndriySvyryd]

• Model building
  • Column name overrides
  • Runtime model
  • Compiled model
  • Relational model
• Migrations
  • Snapshot
  • Seeding
• Update
• Query
• Tests
  • Non-PK columns duplicated across tables
  • Concurrency tokens
  • Customizing linking FK (By default it's required dependent)
  • Views
  • With triggers and owned types
  • With table splitting

API proposal:

modelBuilder.Entity<Customer>().SplitToTable("CustomerDetails", tb =>
{
    // PK mapped to all tables by default

    // Any other property mapped to a split table is not mapped to the default table
    tb.Property(c => c.AlternateKey);

	// Empty column name effectively removes the property from the mapping fragment
    tb.Property(c => c.AlternateKey).HasColumnName("");
});

modelBuilder.Entity<Customer>().ToTable("Customer", tb =>
{
    // Properties can be explicitly mapped to the default table too
    tb.Property(c => c.AlternateKey);
});

modelBuilder.Entity<Customer>().SplitToView("CustomerView", tb =>
{
    tb.Property(c => c.AlternateKey);
});

[netspark]

Would be very appreciated for implementing this, we have a lot of legacy one-to-one tables in DB which make no sense to treat separately in backend

[jansomers]

Would very much love this feature, also the optional relationships is a must have when implementing entity splitting

[maurei]

Any update? Would love to see this feature incorporated.

[ajcvickers]

@maurei This issue is in the Backlog milestone. This means that it is not going to happen for the 3.0 release. We will re-assess the backlog following the 3.0 release and consider this item at that time. However, keep in mind that there are many other high priority features with which it will be competing for resources.

[GeorgeTsaplin]

I suppose what Owned Entity Types can be used as an alternative for Entity Splitting and it's already implemented at EFCore 2.0.

[OskarKlintrot]

Can I somehow specify that the foreign key is already specified in a table? Right now, EF tells me that I must have the FK in the "main" table but the limitation in the issue descriptions only says that FK won't be created in the database. In my case it's already created, is it still not possible to have the FK in another table?

[ajcvickers]

@OskarKlintrot Please open a new issue and attach a small, runnable project or post a small, runnable code listing that shows what you are attempting and what doesn't work.