Formbase 0.17.0

Pairs with MorphDB 0.14.x. A projection whose declaration has not changed reads only the documents
appended since its last run, with the result a rebuild would have, and a bound field names its value
column and, optionally, which record its value belongs to. Breaking for code that constructs or reads
EntityRef, for HTTP clients that send or read a bound field's target, and for implementers of
IProjectionStore and IProjectionState, which gain a member each.

Changed

• A bound field's target names its value column as ValueField, not KeyField. The old name read
  as a lookup key, and declarations were written that way — KeyField was always the column the value
  comes from. EntityRef(entity, valueField, lookupKey, viaField); on the wire, target.valueField
  replaces target.keyField. Declarations already stored by an earlier release read back unchanged.
  RelationHint.KeyField (a relation's link field) is unaffected.

Added

• A bound field can say which record its value belongs to. EntityRef.LookupKey (the field on the
  target that identifies a record) and EntityRef.ViaField (the field of this declaration carrying that
  key) — optional, and only as a pair. On the wire, target.lookupKey and target.viaField.
• A target naming a field that does not exist is refused. Every declaration writer (in-memory,
  SQLite, PostgreSQL) refuses a ViaField that is not a field of the same declaration, and a
  ValueField or LookupKey that is not a field of the target form type when that form type is
  declared (DeclaredTargets); the host answers 400 /problems/invalid-declaration. An undeclared
  target is accepted unchecked.
• A projection brings its table forward instead of rebuilding it when only documents were appended.
  When the declaration, table and recorded state are unchanged since the last projection, a run reads
  only the documents appended since its watermark: rows of records they correct or retire are removed,
  their own rows inserted, and the recorded skips updated in place. The table and GET …/projection/skips are what a rebuild would have produced; the cost of a run follows what was
  appended, not the size of the raw stream. A first run, a changed declaration or table, a table left
  in doubt by a failed run, and the first run after upgrading still rebuild. ProjectionResult.Mode
  (and mode on POST …/projection: rebuild or incremental) says which happened; on an
  incremental run the run's counts and skip lists cover the documents it read.
• IProjectionStore.ReplaceRowsAsync (remove rows by record key or document, then insert — idempotent)
  and IProjectionState.ApplyProjectedDeltaAsync (compare-and-set on the recorded watermark, withdraw
  skips by record or document, append new ones). ProjectionSkip.Key and ProjectionFieldSkip.Key
  name the record a skipped document stood for; ProjectionStamp.SkipsKeyed says whether they do.
  SQLite and PostgreSQL state stores add the columns on first use.

Fixed

• Two projections of one form type started at once in one process no longer race: they run one after
  the other. A run that finds the recorded projection moved under it marks it unverified, so the next
  run rebuilds rather than serving a table both runs wrote to.