From aee620d589f8832b375e45e4406867fec111f37e Mon Sep 17 00:00:00 2001
From: Sam Marks <sam@sammarks.me>
Date: Thu, 23 Jan 2020 19:31:30 -0500
Subject: [PATCH] feat: add modifyEdgeFn for edge customization

---
 .nvmrc                                        |  1 +
 README.md                                     | 18 +++++++++++++
 src/builder/index.js                          |  9 +++++--
 .../src/queries/cat/root/cats-connection.js   |  4 +++
 tests/test-app/src/type-defs/cat.js           |  1 +
 .../knex-implementation.test.js               | 26 +++++++++++++++++++
 6 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 .nvmrc

diff --git a/.nvmrc b/.nvmrc
new file mode 100644
index 0000000..f599e28
--- /dev/null
+++ b/.nvmrc
@@ -0,0 +1 @@
+10
diff --git a/README.md b/README.md
index fd63ac2..3e1c4ce 100644
--- a/README.md
+++ b/README.md
@@ -92,6 +92,24 @@ database column name is "created_at" and the column name on the model is "create
   ```
 </details>
 
+#### Customizing Edges
+
+If you have additional metadata you would like to pass along with each edge, as is allowed by the Relay
+specification, you may do so using the `modifyEdgeFn` option:
+
+```javascript
+const result = await paginate(
+  baseQuery,
+  { first, last, before, after, orderBy, orderDirection },
+  {
+    modifyEdgeFn: (edge) => ({
+      ...edge,
+      custom: 'foo',
+    })
+  }
+);
+```
+
 ### Creating your own connector
 
 Only Knex.js is implemented for now. If you want to connect to a different ORM, you must make your own connector.
diff --git a/src/builder/index.js b/src/builder/index.js
index 6069cc0..7d318e1 100644
--- a/src/builder/index.js
+++ b/src/builder/index.js
@@ -109,7 +109,9 @@ const apolloCursorPaginationBuilder = ({
   },
   opts = {},
 ) => {
-  const { isAggregateFn, formatColumnFn, skipTotalCount = false } = opts;
+  const {
+    isAggregateFn, formatColumnFn, skipTotalCount = false, modifyEdgeFn,
+  } = opts;
   let {
     orderColumn, ascOrDesc,
   } = opts;
@@ -146,11 +148,14 @@ const apolloCursorPaginationBuilder = ({
     getNodesLength,
   });
 
-  const edges = convertNodesToEdges(nodes, {
+  let edges = convertNodesToEdges(nodes, {
     before, after, first, last,
   }, {
     orderColumn, ascOrDesc, isAggregateFn, formatColumnFn,
   });
+  if (modifyEdgeFn) {
+    edges = edges.map(edge => modifyEdgeFn(edge));
+  }
 
   const startCursor = edges[0] && edges[0].cursor;
   const endCursor = edges[edges.length - 1] && edges[edges.length - 1].cursor;
diff --git a/tests/test-app/src/queries/cat/root/cats-connection.js b/tests/test-app/src/queries/cat/root/cats-connection.js
index 6d1c9b8..99122a9 100644
--- a/tests/test-app/src/queries/cat/root/cats-connection.js
+++ b/tests/test-app/src/queries/cat/root/cats-connection.js
@@ -22,6 +22,10 @@ export default async (_, args) => {
     {
       isAggregateFn: column => column === 'idsum',
       formatColumnFn: column => (column === 'idsum' ? Cat.knex().raw('sum(id)') : column),
+      modifyEdgeFn: edge => ({
+        ...edge,
+        custom: 'foo',
+      }),
     },
   );
   return result;
diff --git a/tests/test-app/src/type-defs/cat.js b/tests/test-app/src/type-defs/cat.js
index 65b6fa8..3b8b9c9 100644
--- a/tests/test-app/src/type-defs/cat.js
+++ b/tests/test-app/src/type-defs/cat.js
@@ -14,6 +14,7 @@ const Cat = `
   type CatEdge {
     cursor: String!
     node: Cat!
+    custom: String
   }
 
   enum OrderDirection {
diff --git a/tests/test-app/tests/apollo-cursor-pagination/knex-implementation.test.js b/tests/test-app/tests/apollo-cursor-pagination/knex-implementation.test.js
index f73ebae..bbb7cc1 100644
--- a/tests/test-app/tests/apollo-cursor-pagination/knex-implementation.test.js
+++ b/tests/test-app/tests/apollo-cursor-pagination/knex-implementation.test.js
@@ -678,4 +678,30 @@ describe('getCatsByOwner root query', () => {
       expect(response2.body.data.catsConnection.edges[1].node.lastName).not.toEqual(null);
     });
   });
+
+  describe('modifyEdgeFn', () => {
+    it('modifies edges per the callback', async () => {
+      const query = `
+        {
+          catsConnection(first: 2) {
+            edges {
+              cursor
+              node {
+                id
+                name
+              }
+              custom
+            }
+          }
+        }
+      `;
+      const response = await graphqlQuery(app, query);
+      expect(response.body.errors).not.toBeDefined();
+      expect(response.body.data.catsConnection.edges).toHaveLength(2);
+      expect(response.body.data.catsConnection.edges.map(edge => edge.node.name))
+        .toEqual([cat1.name, cat2.name]);
+      expect(response.body.data.catsConnection.edges.map(edge => edge.custom))
+        .toEqual(['foo', 'foo']);
+    });
+  });
 });