Mapping attribute for IsUnicode

[IanKemp]

What problem are you trying to solve?

We prefer to configure our entities via properties on the entities themselves, as opposed to using the fluent syntax, because we've found it makes the code more readable. However, because not every method on PropertyBuilder has an associated attribute (e.g. IsUnicode), it's not possible to use this approach - so we either have to use a half-half approach, or go full fluent; neither of which are desirable.

Describe the solution you'd like

Add attributes that mirror all available methods exposed by PropertyBuilder and result in the same behaviour.

This would have the additional benefit that EF would no longer have to rely on (mis)-using the attributes in the System.Data.DataAnnotations namespace, which are rather... overloaded at this point. That would make it easier for people to transition between fluent syntax and attributes, without needing an entire article to inform users how to map between both ways.

[ajcvickers]

Duplicate of #10864

[smitpatel]

Design questions for @dotnet/efteam

• Unicode attribute can be specified on any property/field/parameter. Do we need parameter support at present? We don't recognize it anywhere.
• The XML docs refers that it can be set on string properties only. Should it be string equivalent on server side? e.g. JSON converted to string using value converter, can/should user specify IsUnicode for it? In annotation? In Fluent API?
• In scaffolding do we print out Unicode if the value is going to be default value for strings (true).
  Unrelated to UnicodeAttribute.
• Do we want ordering of annotations printed on entity type/properties in scaffolded code?

[smitpatel]

• Specified on property. Field if convention pick it up by default once the field is mapped. Parameter support is deferred till we need it.
• XML docs should be consistent with IsUnicode fluent API.
• Scaffolding should not print attribute if default value
• Keep current ordering.

[smitpatel]

Fixed in #22514

[IanKemp]

Thanks guys!