Support filter expressions in filter param

[adamhenson]

Summary

Currently we accept a filter argument as an array of strings.

ghost-graphql/packages/ghost-graphql/src/resolverCreators/createResourceConnectionResolver.ts

Line 23 in a61e740

filter: { type: new GraphQLList(GraphQLString) },

This is mistakenly prescriptive in that it generates a filter expression with commas (or operators). See filtering syntax.

For example, let's assume we want to get posts that are featured, but are not tagged as tutorial. Assuming the negation operator (-), one may naively come up with an argument like this: filter: ["featured:true", "tag:-tutorial"] (the outcome of not having any other choice).

filter: ["featured:true", "tag:-tutorial"] from our GraphQL query will actually generate a content API query param like so (this would be URI encoded of course):

?filter=featured:true,tag:-tutorial

This is problematic, because in filtering syntax, a comma is actually an "or" operator and our intention was for it to be an "and" like so:

?filter=featured:true+tag:-tutorial

Solution

Support both arrays or a string as a query argument. The array argument should work as it does today and a string argument should be taken literally (this will allow support for filtering syntax).

This support would allow an argument that looks like the below.

filter: "featured:true+tag:-tutorial"

[adamhenson]

Added a filterExpression argument to support this in 24eafff... used like so:

filterExpression: "featured:true+tag:-tutorial"