Proposal: Modify FTS5Pattern to support a mix of AND and OR.

[charlesmchen-bc]

FTS5Pattern is great but it's initializers don't cover all cases.

e.g. init?(matchingAnyTokenIn:) covers "foo OR bar" and init?(matchingAllTokensIn:) covers "foo AND bar", but what about: "(foo OR bar) AND other"?

In some cases you want a single pattern that does all of your matching, e.g. ColumnExpression.match(_ pattern: GRDB.FTS5Pattern).

Proposal 1:

extension FTS5Pattern
   static func allOf(_ patterns: [FTS5Pattern]) -> FTS5Pattern 
   static func anyOf(_ patterns: [FTS5Pattern]) -> FTS5Pattern 

"(foo OR bar) AND other" could be expressed like so:

FTS5Pattern.allOf([
   .init(matchingAnyTokenIn:"foo bar"),
   .init(matchingAnyTokenIn:"other"),
])

Proposal 2:
Expose a FTS5Pattern .initializer that takes rawPattern as an escape hatch, so that client code can construct the pattern.

If you consider either proposal a good idea, I could prepare a PR.

Thanks for all of your hard work @groue .

[groue]

Hello @charlesmchen-bc, and thank you!

If you have access to a database connection, you can combine other patterns with makeFTS5Pattern(rawPattern:forTable:):

func fetchDocuments(_ db: Database) throws -> [Document] {
  let pattern1: FTS5Pattern = ...
  let pattern2: FTS5Pattern = ...
  let combinedRawPattern = "(\(pattern1.rawPattern)) OR (\(pattern2.rawPattern))"
  let combinedPattern = try db.makeFTS5Pattern(rawPattern: combinedRawPattern, forTable: "document")
  return try Document.matching(combinedPattern)
}

As you see, a database connection is required in order to build a FTS5Pattern from a raw string. The goal was to validate FTS5 Column Filters and to fail early, at the pattern creation, instead of failing when the request is executed. Retrospectively, this was probably a mistake, because it is not very handy to have to wait for a connection.

Will you please tell if you can use this technique? If not, we'll relax the api. Your first proposal is interesting as well 👍