Using Schema - HackMD

--- title: Using Schema tags: ytt,schema --- # Using Schema ytt v0.37.0 (what ever the playground is at this point 1/21/21) this is before some of the any type bugs were fixed??? - `null` values in a schema or schema overlays are not allowed unless the type is `any` - even if a data value is `nullable` in the base schema, - and a schema overlay sets that `nullable` data value to null, - then the schema overlay will not be a valid schema. - Common ways that you can invoke a schema overlay - another schema file in the same library - another schema file in a different library with `@library/ref` - yaml fragment provided to a library via `library.with_data_values_schema()` - Facts about schema overlays - add keys with `@overlay/match missing_ok=True` - `@schema` annotations are processed during the individual checks of the schema files, - but are not carried over during the overlay, so they have no lasting effects. - values can not be null, even if annotated with `@schema/type any=True` - `@schema/type any=True` - when the value is `null` ANYTHING can be overlayed into this value from a schema overlay # `@schema` annotations ### `@schema/nullable` - allows null value and sets null as default value ### `@schema/type` - sets type of value for the node it annotates - `any=True` - removes schema checking from this node's value, recursively - short circuits schema processing, so any value that is there will be in the data values - errors when other schema annotations are nested. - good way to add keys in data values under a data value that is any type ### `@schema/default` - sets the default value for the node it annotates - accepts a starlark value - value can be defined by the result of a function - predominantly used over map items that contain arrays, since arrays by default are empty (remember that arrays append items by default) - cannot be `None` or `null` unless combined with `@schema/nullable` (which is then redundant) - otherwise when used with `@schema/nullable`, the `@schema/default` value is the default value ### Documentation annotations - `@schema/title` - `@schema/description` - `@schema/examples` - `@schema/depreciated` # Open Questions - Q: when overlaying Schema, is it possible to redefine a data value (i.e. replace from the "right" over the "left"?) - Q: if someone cannot edit the schema or write a schema overlay, but they want to provide a new data value, what are their options?