Installation

npm install -S graphql-query-complexity

Usage

import{createComplexityRule,simpleEstimator}from'graphql-query-complexity';construle=createComplexityRule({// The maximum allowed query complexity, queries above this threshold will be rejectedmaximumComplexity:1_000,// The query variables. This is needed because the variables are not available// in the visitor of the graphql-js libraryvariables:{},// The context object for the request (optional)context:{}// Specify operation name when evaluating multi-operation documentsoperationName?:string,// The maximum number of query nodes to evaluate (fields, fragments, composite types).// If a query contains more than the specified number of nodes, the complexity rule will// throw an error, regardless of the complexity of the query.//// Default: 10_000maxQueryNodes?:10_000,// Optional callback function to retrieve the determined query complexity// Will be invoked whether the query is rejected or not// This can be used for logging or to implement rate limitingonComplete:(complexity:number)=>{console.log('Determined query complexity: ',complexity)},// Optional function to create a custom errorcreateError:(max:number,actual:number)=>{returnnewGraphQLError(`Query is too complex:${actual}. Maximum allowed complexity:${max}`);},// Add any number of estimators. The estimators are invoked in order, the first// numeric value that is being returned by an estimator is used as the field complexity.// If no estimator returns a value, an exception is raised.estimators:[// Add more estimators here...// This will assign each field a complexity of 1 if no other estimator// returned a value.simpleEstimator({defaultComplexity:1})]});

Configuration / Complexity Estimators

Creating Custom Estimators

typeComplexityEstimatorArgs={// The composite type (interface, object, union) that the evaluated field belongs totype:GraphQLCompositeType;// The GraphQLField that is being evaluatedfield:GraphQLField<any,any>;// The GraphQL node that is being evaluatednode:FieldNode;// The input arguments of the fieldargs:{[key:string]:any};// The complexity of all child selections for that fieldchildComplexity:number;// The context object for the request if it was providedcontext?:Record<string,any>;};typeComplexityEstimator=(options:ComplexityEstimatorArgs)=>number|void;

Usage with express-graphql

import{simpleEstimator,createComplexityRule,}from'graphql-query-complexity';importexpressfrom'express';importgraphqlHTTPfrom'express-graphql';importschemafrom'./schema';constapp=express();app.use('/api',graphqlHTTP(async(request,response,{ variables})=>({    schema,validationRules:[createComplexityRule({estimators:[// Configure your estimatorssimpleEstimator({defaultComplexity:1}),],maximumComplexity:1000,        variables,onComplete:(complexity:number)=>{console.log('Query Complexity:',complexity);},}),],})));

Calculate query complexity

import{getComplexity,simpleEstimator}from'graphql-query-complexity';import{parse}from'graphql';// Import your schema or get it form the info object in your resolverimportschemafrom'./schema';// You can also use gql template tag to get the parsed queryconstquery=parse(`  query Q($count: Int) {    some_value    some_list(count: $count) {      some_child_value    }  }`);try{constcomplexity=getComplexity({estimators:[simpleEstimator({defaultComplexity:1})],    schema,    query,variables:{count:10,},});console.log(complexity);// Output: 3}catch(e){// Log error in case complexity cannot be calculated (invalid query, misconfiguration, etc.)console.error('Could not calculate complexity',e.message);}

Prior Art