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