Apply a schema's canonical type declarations to handler output

Schema YAML is the single source of truth for canonical column types. crt_schema_conform() calls this after validation, so every registered (source, file_name) pair gets type enforcement for free — handlers do not encode type knowledge.

Usage

crt_schema_apply(df, schema)

Arguments

df: A data frame.
schema: The parsed schema YAML (a list with canonical$cols).

Value

A tibble with columns coerced to canonical types.

Details

Reads canonical.cols[].type from the schema and coerces each named column to the declared type. Columns present in the data but absent from the schema's canonical.cols are left untouched. Columns absent from the data but declared in the schema are left to crt_schema_validate() to surface (this function does not validate presence — only type when the column exists).

Supported type values:

integer -> as.integer()
double -> as.double()
string -> as.character() (handles readr's Date / POSIXct auto-parsing for columns the schema declares as text)
logical -> as.logical()
datetime -> POSIXct rendered in UTC, see below

datetime is stamped, never converted

A datetime column means an instant, and this function never changes which instant it is. A POSIXct input has its tzone attribute stamped to "UTC", which changes the rendering and nothing else; the epoch is untouched.

That distinction is the whole point of the type. Several readers return correct UTC instants with an empty tzone attribute — GeoPackage DATETIME columns read through sf are the case this was written for — so R renders them in Sys.timezone(). On a UTC-7 machine the same instant prints seven hours earlier than it does from an epoch, which reads as a second clock in a second timezone. Converting to "fix" the rendering injects a real whole-hour error into every downstream join; stamping fixes the label, which is all that was ever wrong.

Other inputs:

numeric is read as epoch seconds
Date is read as UTC midnight. Note as.POSIXct() silently ignores tz for a Date, converting in the system zone instead, so this goes through format() first — west of UTC the naive call moves the day boundary.
character is parsed as ISO 8601 in UTC, accepting a T separator and a trailing Z