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5.1. Use `filter` argument to filter list

Consider two approaches to organizing filtering. One where all arguments are on the same level:

type Query {
  articles(authorId: Int, tags: [String], lang: LangEnum): [Article]

and another one where there is a single argument filter of type ArticleFilter:

type Query {
  articles(filter: ArticleFilter): [Article]

input ArticleFilter {
  authorId: Int
  tags: [String]
  lang: LangEnum

Combining filter options inside one filter argument of type ArticleFilter is better. Here is why:

  • non-filter arguments (e.g. sorting, limit, offset, page number, cursor, language) are clearly separated from filter arguments
  • consumers will get a ArticleFilter type for static analysis. This also reduces the likelihood of errors on the client
  • it's much easier to reason about GraphQL API when fields have a small number of 3-5 arguments. You can locate the filter argument and drill down into the available options
  • the same filter type can be reused in other places where articles (or other objects) are requested

Having a consistent name for a filter field across the schema is important. Without a standard teams can introduce multiple names in the same API such as filter, where, condition and f based on their background. Given that there are SQL and NoSQL databases, caches and other services, then the most appropriate name for the filtering argument is filter . It is clear and suitable for everyone! While where better suits Backend engineers that got used to SQL terms.