Merge pull request #20 from slicknode/feature/field-extension-estimator

Field extension estimator #19

Author: ivome

README.md

@@ -74,9 +74,11 @@ or write your own:
     last estimator in the chain for a default value.
 *   **[`directiveEstimator`](src/estimators/directive/README.md):** Set the complexity via a directive in your 
     schema definition (for example via GraphQL SDL)
-*   **[`fieldConfigEstimator`](src/estimators/fieldConfig/README.md):** The field config estimator lets you set a numeric value or a custom estimator
+*   **[`fieldExtensionsEstimator`](src/estimators/fieldExtensions/README.md):** The field extensions estimator lets you set a numeric value or a custom estimator
+    function in the field config extensions of your schema. 
+*   **[`fieldConfigEstimator`](src/estimators/fieldConfig/README.md):** (DEPRECATED) The field config estimator lets you set a numeric value or a custom estimator
     function in the field config of your schema. 
-*   **[`legacyEstimator`](src/estimators/legacy/README.md):** The legacy estimator implements the logic of previous versions. Can be used
+*   **[`legacyEstimator`](src/estimators/legacy/README.md):** (DEPRECATED) The legacy estimator implements the logic of previous versions. Can be used
     to gradually migrate your codebase to new estimators. 
 *   PRs welcome...
 

src/estimators/fieldConfig/index.ts

@@ -1,6 +1,13 @@
 import {ComplexityEstimator, ComplexityEstimatorArgs} from '../../QueryComplexity';
 
+/**
+ * @deprecated Use fieldExtensionsEstimator instead
+ */
 export default function (): ComplexityEstimator {
+  console.warn(
+    'DEPRECATION WARNING: fieldConfigEstimator is deprecated. Use fieldExtensionsEstimator instead'
+  );
+
   return (args: ComplexityEstimatorArgs) => {
     // Calculate complexity score
     if (typeof args.field.complexity === 'number') {

src/estimators/fieldExtensions/README.md

@@ -0,0 +1,97 @@
+# Field Extensions Estimator
+
+The `fieldExtensionsEstimator` lets you define a numeric value or a custom estimator
+in the field config extensions of your GraphQL schema. If no complexity is set in the field config,
+the estimator does not return any value and the next estimator in the chain is executed. 
+
+## Usage
+
+```typescript
+import queryComplexity, {
+  fieldExtensionsEstimator,
+  simpleEstimator
+} from 'graphql-query-complexity';
+
+const rule = queryComplexity({
+  estimators: [
+    fieldExtensionsEstimator(),
+    
+    // We use the simpleEstimator as fallback so we only need to 
+    // define the complexity for non 1 values (this is not required...)
+    simpleEstimator({defaultComplexity: 1})
+  ]
+  // ... other config
+});
+```
+
+You can set a custom complexity as a numeric value in the field config:
+
+```javascript
+const Post = new GraphQLObjectType({
+  name: 'Post',
+  fields: () => ({
+    title: { type: GraphQLString },
+    text: {
+      type: GraphQLString,
+      extensions: {
+        complexity: 5
+      },
+    },
+  }),
+});
+```
+
+**Example Query:**
+
+```graphql
+query {
+  posts(count: 10) {
+    title
+    text
+  }
+}
+```
+
+This query would result in a complexity of 7. 
+5 for the `text` field and 1 for each of the other fields. 
+
+You can also pass an estimator in the field config to determine a custom complexity. 
+This function will provide the complexity of the child nodes as well as the field input arguments.
+
+The function signature is the same as for the main estimator which lets you reuse estimators:
+
+```typescript
+type ComplexityEstimatorArgs = {
+  type: GraphQLCompositeType,
+  field: GraphQLField<any, any>,
+  args: {[key: string]: any},
+  childComplexity: number
+}
+
+type ComplexityEstimator = (options: ComplexityEstimatorArgs) => number | void;
+```
+
+That way you can make a more realistic estimation of individual field complexity values:
+
+```javascript
+const Query = new GraphQLObjectType({
+  name: 'Query',
+  fields: () => ({
+    posts: {
+      type: new GraphQLList(Post),
+      args: {
+        count: {
+          type: GraphQLInt,
+          defaultValue: 10
+        }
+      },
+      extensions: {
+        complexity: ({args, childComplexity}) => childComplexity * args.count,
+      },
+    },
+  }),
+});
+```
+
+This would result in a complexity of 60 since the `childComplexity` of posts (`text` 5, `title` 1) is multiplied by the
+number of posts (`args.count`).