Efcore: Add HasPrecision() Fluent API

[bricelam]

Our type mapping supports precision and scale. We should add back EF6's HasPrecision() method on PropertyBuilder.

[slorion]

Any ETA on this feature? Or any way to do it in a database agnostic way currently? Having to tie up model creation to a particular database solely because of this missing piece is quite annoying.

[whizkidwwe1217]

Is this gonna be shipped in 2.2.+?

[ajcvickers]

@whizkidwwe1217 If you mean in a patch of 2.2, then no. If you mean in 3.0 or later, then that is the plan.

[bricelam]

Note to implementer: Don't forget to...

• Flow these through MigrationsSqlGenerator.GetColumnType()
• Add them to ColumnOperation, MigrationsBuilder.Add/AlterColumn, and ColumnsBuilder.Column
• Serialize it into ModelSnapshot
• Diff it in MigrationsModelDiffer

[bricelam]

SQL Server notes:

Data type | Default precision | Default scale
--- | ---:| ---:
datetime2 | 7 | (n/a)
datetimeoffset | 7 | (n/a)
decimal | 18 | 0
float | 53 | (n/a)
numeric | 18 | 0
time | (n/a) | 7

[codeoflin]

how to use it in "netcoreapp2.2"?

[whizkidwwe1217]

I think they're planning to implement it in 3.0 but we really need this in 2.2. @ajcvickers @bricelam

[smitpatel]

You can always specify full type using HasColumnType. This would be a good sugar to add but not a blocker in any sense.

[SARAVANA1501]

@bricelam I am interested in working on it, Will you be able to provide more implementation details?

[bricelam]

Look at the IsUnicode or HasMaxLength code for an end-to-end example

[bricelam]

And yes, feel free to open a draft PR if you get stuck or have implementation questions

[AndriySvyryd]

@SARAVANA1501 RelationalTypeMappingSource should also be updated to account for this.

[lajones]

@dotnet/efcore Throughout a lot of the current code precision and scale are treated as ints. But EF6's HasPrecision(precision, scale) treated them as bytes. and so does DbParameter.
Should I update all our code to use byte or simply cast to byte when I need a DbParameter? My preference is the former but wanted to make sure because it's in a lot of places.

[AndriySvyryd]

@lajones This API is defined in Core, so DbParameter isn't that relevant. We usually stick to int unless there's a good reason not to even if the value will never be larger than Byte.Max

[lajones]

@AndriySvyryd I'm updating SqlServerDecimalTypeMapping.ConfigureParameter to include precision and scale. Currently Precision.Value is an int?, but parameter.Precision requires a byte.

[AndriySvyryd]

Provider implementation should cast as needed.

[lajones]

OK. Will do.

[lajones]

@dotnet/efcore Also would like opinion on what effect HasPrecision(precision) with no scale specified should have on the scale.
SqlServerDecimalTypeMapping's default for a decimal property is decimal(18,2), in particular note that the scale is 2. If I then call e.g. HasPrecision(4) on that property, i.e. I do not specify the scale, should I expect the scale to remain unchanged at 2 or should it change to 0? If you define a column in SqlServer as decimal(4) you expect the precision to be 4 and the scale to be 0, i.e. any time I call just HasPrecision(precision) with no scale then the scale is set to 0. But remember HasPrecision() applies to all providers, not just SqlServer.