alpha.0

.eslintrc.js

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+module.exports = {
+  parserOptions: {
+    sourceType: "module",
+  },
+  extends: ["eslint:recommended", "prettier"],
+  plugins: ["prettier"],
+  env: {
+    node: true,
+    es6: true,
+  },
+  rules: {
+    "prettier/prettier": [
+      "error",
+      {
+        trailingComma: "es5",
+      },
+    ],
+    "comma-dangle": [
+      2,
+      {
+        arrays: "always-multiline",
+        objects: "always-multiline",
+        imports: "always-multiline",
+        exports: "always-multiline",
+        functions: "never",
+      },
+    ],
+    "no-confusing-arrow": 0,
+    "no-else-return": 0,
+    "no-underscore-dangle": 0,
+    "no-unused-vars": [
+      2,
+      {
+        argsIgnorePattern: "^_",
+      },
+    ],
+    "no-restricted-syntax": 0,
+    "no-await-in-loop": 0,
+    camelcase: 0,
+  },
+};

.gitattributes

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+* text=auto

.gitignore

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+node_modules

README.md

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+[![Package on npm](https://img.shields.io/npm/v/postgraphile-plugin-derived-field.svg)](https://www.npmjs.com/package/postgraphile-plugin-derived-field)
+
 # postgraphile-plugin-derived-field
-Add derived fields in PostGraphile
+This plugin adds derived fields in PostGraphile v4.
+
+> **Note:** This plugin targets the beta release of PostGraphile v4.
+
+## Getting Started
+
+``` js
+const express = require("express");
+const { postgraphile } = require("postgraphile");
+const PostGraphileDerivedFieldPlugin = require("postgraphile-plugin-derived-field");
+
+const app = express();
+
+const AWS = require("aws-sdk");
+const s3 = new AWS.S3();
+const bucket = "postgraphile-plugin-test";
+
+app.use(
+  postgraphile(pgConfig, schema, {
+    graphiql: true,
+    appendPlugins: [PostGraphileDerivedFieldPlugin],
+    graphileBuildOptions: {
+      derivedFieldDefinitions: [
+        {
+          identifiers: ["my_schema.my_table.my_column"],
+          inflect: (fieldName) => `${fieldName}Derived`,
+          resolve: (val) => `Value derived from ${val}`
+        }
+      ]
+    }
+  })
+);
+
+app.listen(5000);
+```
+
+## Examples
+
+<details>
+
+<summary>Generate pre-signed URLs for client-side S3 GET requests</summary>
+
+``` js
+const express = require("express");
+const { postgraphile } = require("postgraphile");
+const PostGraphileDerivedFieldPlugin = require("postgraphile-plugin-derived-field");
+
+const AWS = require("aws-sdk");
+const s3 = new AWS.S3();
+const bucket = "postgraphile-plugin-test";
+
+const app = express();
+
+app.use(
+  postgraphile(pgConfig, schema, {
+    graphiql: true,
+    appendPlugins: [PostGraphileDerivedFieldPlugin],
+    graphileBuildOptions: {
+      derivedFieldDefinitions: [
+        {
+          identifiers: ["my_schema.my_table.my_column"],
+          inflect: (fieldName) => `${fieldName}Url`,
+          resolve: (val) => s3.getSignedUrl('getObject', {Bucket: bucket, Key: val, Expires: 900})
+        }
+      ]
+    }
+  })
+);
+
+app.listen(5000);
+```
+
+</details>

index.js

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+module.exports = function PostGraphileDerivedFieldPlugin(builder, options) {
+  require("./src/DerivedFieldPlugin.js")(builder, options);
+};

package.json

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+{
+  "name": "postgraphile-plugin-derived-field",
+  "version": "1.0.0-alpha.0",
+  "description": "Add derived fields in PostGraphile",
+  "main": "index.js",
+  "scripts": {
+    "test": "scripts/test"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/mattbretl/postgraphile-plugin-derived-field.git"
+  },
+  "author": "Matt Bretl",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/mattbretl/postgraphile-plugin-derived-field/issues"
+  },
+  "dependencies": {},
+  "peerDependencies": {
+    "postgraphile": "^4.0.0-beta.0"
+  },
+  "devDependencies": {
+    "eslint": "^4.0.0",
+    "eslint-config-prettier": "2.3.0",
+    "eslint-plugin-jest": "^20.0.3",
+    "eslint-plugin-prettier": "^2.1.2",
+    "graphql": "^0.10.5",
+    "jest": "^20.0.4",
+    "pg": ">=6.1.0 <8",
+    "postgraphile-core": "^4.0.0-beta.0",
+    "prettier": "^1.4.4"
+  },
+  "jest": {
+    "testRegex": "__tests__/.*\\.test\\.js$"
+  },
+  "files": [
+    "src"
+  ]
+}

src/DerivedFieldPlugin.js

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+function DerivedFieldPlugin(
+  builder,
+  { pgInflection: inflection, derivedFieldDefinitions }
+) {
+  builder.hook("GraphQLObjectType:fields", (fields, build, context) => {
+    const {
+      extend,
+      pgIntrospectionResultsByKind: introspectionResultsByKind,
+      graphql: { GraphQLString },
+      pgColumnFilter,
+      fieldDataGeneratorsByFieldNameByType,
+    } = build;
+    const {
+      scope: { pgIntrospection: table, isPgRowType },
+      fieldWithHooks,
+      Self,
+    } = context;
+
+    if (
+      !isPgRowType ||
+      !table ||
+      table.kind !== "class" ||
+      derivedFieldDefinitions == null
+    ) {
+      return fields;
+    }
+
+    const tableType = introspectionResultsByKind.type.filter(
+      type =>
+        type.type === "c" &&
+        type.namespaceId === table.namespaceId &&
+        type.classId === table.id
+    )[0];
+    if (!tableType) {
+      throw new Error("Could not determine the type for this table");
+    }
+
+    const derivedFields = introspectionResultsByKind.attribute
+      .filter(attr => attr.classId === table.id)
+      .filter(attr => pgColumnFilter(attr, build, context))
+      .reduce((memo, attr) => {
+        for (let def of derivedFieldDefinitions) {
+          if (
+            def.identifiers.includes(
+              `${table.namespaceName}.${table.name}.${attr.name}`
+            )
+          ) {
+            const fieldName = inflection.column(
+              attr.name,
+              table.name,
+              table.namespaceName
+            );
+            const derivedFieldName = def.inflect(fieldName);
+            if (memo[derivedFieldName]) {
+              throw new Error(
+                `Derived field '${derivedFieldName}' conflicts with existing GraphQL field`
+              );
+            }
+            const field = fields[fieldName];
+            const { resolve: oldResolve } = field;
+            memo[derivedFieldName] = fieldWithHooks(
+              derivedFieldName,
+              ({ addDataGenerator }) => {
+                const generatorsByField = fieldDataGeneratorsByFieldNameByType.get(
+                  Self
+                );
+                generatorsByField[fieldName].forEach(g => {
+                  addDataGenerator(g);
+                });
+                return {
+                  type: def.returnType || GraphQLString,
+                  resolve: (...resolveParams) => {
+                    const val = oldResolve(...resolveParams);
+                    return def.resolve(val);
+                  },
+                };
+              },
+              { pgFieldIntrospection: attr }
+            );
+          }
+        }
+        return memo;
+      }, {});
+
+    return extend(
+      fields,
+      derivedFields,
+      `Adding derived field to '${Self.name}'`
+    );
+  });
+}
+
+module.exports = DerivedFieldPlugin;