CODEWITHSUNDEEP
graphql
Robert
Robert

Reputation: 190

How to define and execute GraphQL query with filter

So the thing i try to do is, retrieve filtered data from the Database (MongoDB in my situation) using GraphQL.

Speaking in "MySQL language" how to implement the where clause in GraphQL?

I followed this tutorial : https://learngraphql.com/basics/using-a-real-data-source/5

Query with filter was defined like this : 

const Query = new GraphQLObjectType({
  name: "Queries",
  fields: {
    authors: {
      type: new GraphQLList(Author),
      resolve: function(rootValue, args, info) {
        let fields = {};
        let fieldASTs = info.fieldASTs;
        fieldASTs[0].selectionSet.selections.map(function(selection) {
          fields[selection.name.value] = 1;
        });
        return db.authors.find({}, fields).toArray();
      }
    }
  }
});

The tricky part here is the info parameter in the resolve function. Some explanations i've found here : http://pcarion.com/2015/09/26/graphql-resolve/

So it is AST (Abstract Syntax Tree)

Can anyone please provide some basic real-life example code that would show how to define and execute the following query : Get all authors where name == John

Thank you!

Upvotes: 1

Views: 3859

Answers (1)

Andy Carlson
Andy Carlson

Reputation: 3909

There is no need to examine the AST. That would be awfully laborious.

All you need to do is define an argument on the author field. This is the second paramenter of the resolver, so you can check for that arguement and include it in the Mongo query.

const Query = new GraphQLObjectType({
  name: "Queries",
  fields: {
    authors: {
      type: new GraphQLList(Author),

      // define the arguments and their types here
      args: {
        name: { type: GraphQLString }
      },

      resolve: function(rootValue, args, info) {
        let fields = {};
        // and now you can check what the arguments' values are
        if (args.name) {
          fields.name = args.name
        }
        // and use it when constructing the query
        return db.authors.find(fields, fields).toArray();
      }
    }
  }
});

Upvotes: 2

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