我正在使用一个模式指令，它实现了SchemaDirectiveVisitor的visitFieldDefition函数。我想知道模式中定义的字段的类型，例如该类型是否是数组。
在架构中：
type DisplayProperties {
description: StringProperty @property
descriptions: [StringProperty]! @property
}
属性指令：
class PropertyDirective extends SchemaDirectiveVisitor {
visitFieldDefinition(field) {
// how to check that field type is StringProperty?
// how to find out that the field type is an array?
}
}
使用Apollo服务器和graph ql工具。
传递给visitFieldDefition的第一个参数是一个GraphQLField对象：
interface GraphQLField<TSource, TContext, TArgs = { [key: string]: any }> {
name: string;
description: Maybe<string>;
type: GraphQLOutputType;
args: GraphQLArgument[];
resolve?: GraphQLFieldResolver<TSource, TContext, TArgs>;
subscribe?: GraphQLFieldResolver<TSource, TContext, TArgs>;
isDeprecated?: boolean;
deprecationReason?: Maybe<string>;
astNode?: Maybe<FieldDefinitionNode>;
}
因此，要获得类型，您只需执行以下操作：
const type = field.type
如果该字段非空、列表或两者的某种组合，则需要“展开”该类型。您可以随时检查是否有任何包装类型是List：
const { isWrappingType } = require('graphql')
let isList = false
let type = field.type
while (isWrappingType(type)) {
if (type.name === 'GraphQLList') {
isList = true
}
type = type.ofType
}
我们可以检查graph ql类型
const { GraphQLString } = require('graphql');
const type = field.type
if(field.type === GraphQLString) return 'string'
我如何使用它？我需要用S3根前缀S3对象键URL所以我创建了一个指令来执行此操作，它检查并返回条件字符串和数组。和代码。
const { SchemaDirectiveVisitor } = require('apollo-server');
const { defaultFieldResolver, GraphQLString, GraphQLList } = require('graphql');
class S3Prefix extends SchemaDirectiveVisitor {
visitFieldDefinition(field) {
const { resolve = defaultFieldResolver } = field;
field.resolve = async function (...args) {
const result = await resolve.apply(this, args);
if (field.type === GraphQLString) {
if (result) {
return [process.env.AWS_S3_PREFIX, result].join('');
} else {
return null;
}
}
if (field.type === GraphQLList) {
if (result) {
return result.map((key) => [process.env.AWS_S3_PREFIX, key].join(''));
} else {
return [];
}
}
};
}
}
module.exports = S3Prefix;
