如何在嵌套查询的解析器函数中传递根参数？[英] How to pass root parameters in the resolver function of a nested query?

问题描述

I have a query of the following nature

Category1(name: $cat1){
   Category2(secondName: $cat2){
      secondName
    }}

My schema is like so:

const Query = new GraphQLObjectType({
name: 'Query',
fields: {
    Category1: {
        type: new GraphQLList(Category1Type),
        args: { name },
        resolve: resolveCategory1
    }}
})

And then the Category1Type is defined as:

const Category1Type = new GraphQLObjectType({
    name: 'Category1',
    description: '<>',
    fields: () => ({
        name: { type: GraphQLString },
        category2: {
            type: new GraphQLList(CategoryType2),
            args: { secondName },
            resolve: resolveCategory2
        }
    })
});

For simplicity sake, assume category2 is like so:

const Category2Type = new GraphQLObjectType({
    name: 'Category2',
    description: '<>',
    fields: () => ({
        name: { type: GraphQLString },
    })
});

Now I want to fetch all Category2 items under Category1 with option to filter, like so:

Category1(name: $name){
   name
   category2(name: $name){
      name 
}}

My resolvers are defined like so:

    # Category1 resolver
    function cat1resolve (root, args) {
return SELECT * from data WHERE category1_name = args.name
}

    # Category2 resolver
    function cat2Resolve (root, args) {
return SELECT * from data WHERE category1_name = rootargs.name and categort2_name = args.secondName }

Now the problem is that the 'resolver' for cat2Resolve is not able to see or receive the rootargs.name for me to do this kind of filtering.

推荐答案

The resolve function signature includes 4 parameters. From Apollo's docs:

1. obj: The object that contains the result returned from the resolver on the parent field, or, in the case of a top-level Query field, the rootValue passed from the server configuration. This argument enables the nested nature of GraphQL queries.
2. args: An object with the arguments passed into the field in the query. For example, if the field was called with author(name: "Ada"), the args object would be: { "name": "Ada" }.
3. context: This is an object shared by all resolvers in a particular query, and is used to contain per-request state, including authentication information, dataloader instances, and anything else that should be taken into account when resolving the query. If you’re using Apollo Server, read about how to set the context in the setup documentation.
4. info: This argument should only be used in advanced cases, but it contains information about the execution state of the query, including the field name, path to the field from the root, and more. It’s only documented in the GraphQL.js source code.

Note: These docs are for graphql-tools' makeExecutableSchema (which I highly recommend) but the same applies to plain old GraphQL.JS.

The key point here is that a resolver for a particular field is generally agnostic to what other resolvers do or what information is passed to them. It's handed its own parent field value, its own arguments, the context and expected to work with that.

However, there is a workaround utilizing the info parameter. The object passed to info is huge and can be complicated to parse, but contains virtually all the information about the requested query itself. There are libraries out to help with parsing it, but you may want to print the whole thing to console and poke around (it's pretty cool!).

Using something like lodash's get, we can then do:

const category1id = get(info, 'operation.selectionSet.selections[0].arguments[0].value.value')

and utilize that value inside your query. The above is pretty fragile, since it assumes your request only contains the one query, and you only have one argument on the Category1 field. In practice, you'd probably want to utilize Array.find and look up the fields/arguments by name, but this should give you a starting point.