Calculating query complexity

README.md

@@ -104,6 +104,33 @@ type ComplexityEstimatorArgs = {
 type ComplexityEstimator = (options: ComplexityEstimatorArgs) => number | void;
 ```
 
+## Calculate query complexity
+```javascript
+import { calculateComplexity, simpleEstimator } from "graphql-query-complexity/dist/QueryComplexity";
+import { parse } from 'graphql';
+
+// In a resolver the schema can be retrieved from the info argument.
+const schema = undefined; 
+const query = parse(`
+ query {
+ some_value
+ some_list(count: 10) {
+ some_child_value
+ }
+ }
+`);
+
+const complexity = calculateComplexity({
+ estimators: [
+ simpleEstimator({defaultComplexity: 1})
+ ],
+ schema,
+ query
+});
+
+console.log(complexity); // Output: 3
+```
+
 ## Usage with express-graphql
 
 To use the query complexity analysis validation rule with express-graphql, use something like the

src/QueryComplexity.ts

@@ -15,6 +15,8 @@ import {
  InlineFragmentNode,
  assertCompositeType,
  GraphQLField, isCompositeType, GraphQLCompositeType, GraphQLFieldMap,
+ GraphQLSchema, DocumentNode, TypeInfo,
+ visit, visitWithTypeInfo
 } from 'graphql';
 import {
  GraphQLUnionType,
@@ -74,6 +76,26 @@ function queryComplexityMessage(max: number, actual: number): string {
  );
 }
 
+export function calculateComplexity(options: {
+ estimators: ComplexityEstimator[],
+ schema: GraphQLSchema,
+ query: DocumentNode,
+ variables?: Object
+}): number {
+ const typeInfo = new TypeInfo(options.schema);
+
+ const context = new ValidationContext(options.schema, options.query, typeInfo);
+ const visitor = new QueryComplexity(context, {
+ // Maximum complexity does not matter since we're only interested in the calculated complexity.
+ maximumComplexity: Infinity,
+ estimators: options.estimators,
+ variables: options.variables
+ });
+
+ visit(options.query, visitWithTypeInfo(typeInfo, visitor));
+ return visitor.complexity;
+}
+
 export default class QueryComplexity {
  context: ValidationContext;
  complexity: number;

src/__tests__/QueryComplexity-test.ts

@@ -14,7 +14,7 @@ import {expect} from 'chai';
 
 import schema from './fixtures/schema';
 
-import ComplexityVisitor from '../QueryComplexity';
+import ComplexityVisitor, {calculateComplexity} from '../QueryComplexity';
 import {
  simpleEstimator,
  fieldConfigEstimator,
@@ -23,6 +23,23 @@ import {
 describe('QueryComplexity analysis', () => {
  const typeInfo = new TypeInfo(schema);
 
+ it('should calculate complexity', () => {
+ const ast = parse(`
+ query {
+ variableScalar(count: 10)
+ }
+ `);
+
+ const complexity = calculateComplexity({
+ estimators: [
+ simpleEstimator({defaultComplexity: 1})
+ ],
+ schema,
+ query: ast
+ });
+ expect(complexity).to.equal(1);
+ });
+
  it('should not allow negative cost', () => {
  const ast = parse(`
  query {