fix(connectionPlugin): allow first and last to be zero (#436)

Co-authored-by: Jason Kuhrt <jason.kuhrt@dialogue.co>

src/plugins/connectionPlugin.ts

@@ -839,12 +839,12 @@ function defaultPageInfoFromNodes(nodes: any[], args: PaginationArgs) {
 function defaultHasNextPage(nodes: any[], args: PaginationArgs) {
   // If we're paginating forward, and we don't have an "after", we'll assume that we don't have
   // a previous page, otherwise we will assume we have one, unless the after cursor === "0".
-  if (args.first) {
+  if (typeof args.first === "number") {
     return nodes.length >= args.first;
   }
   // If we're paginating backward, and there are as many results as we asked for, then we'll assume
   // that we have a previous page
-  if (args.last) {
+  if (typeof args.last === "number") {
     if (args.before && args.before !== "0") {
       return true;
     }
@@ -860,7 +860,7 @@ function defaultHasNextPage(nodes: any[], args: PaginationArgs) {
 function defaultHasPreviousPage(nodes: any[], args: PaginationArgs) {
   // If we're paginating forward, and we don't have an "after", we'll assume that we don't have
   // a previous page, otherwise we will assume we have one, unless the after cursor === "0".
-  if (args.first) {
+  if (typeof args.first === "number") {
     if (args.after && args.after !== "0") {
       return true;
     }
@@ -868,7 +868,7 @@ function defaultHasPreviousPage(nodes: any[], args: PaginationArgs) {
   }
   // If we're paginating backward, and there are as many results as we asked for, then we'll assume
   // that we have a previous page
-  if (args.last) {
+  if (typeof args.last === "number") {
     return nodes.length >= args.last;
   }
   /* istanbul ignore next */
@@ -888,7 +888,7 @@ function defaultCursorFromNode(
   let cursorIndex = index;
   // If we're paginating forward, assume we're incrementing from the offset provided via "after",
   // e.g. [0...20] (first: 5, after: "cursor:5") -> [cursor:6, cursor:7, cursor:8, cursor:9, cursor: 10]
-  if (args.first) {
+  if (typeof args.first === "number") {
     if (args.after) {
       const offset = parseInt(args.after, 10);
       cursorIndex = offset + index + 1;
@@ -897,7 +897,7 @@ function defaultCursorFromNode(
 
   // If we're paginating backward, assume we're working backward from the assumed length
   // e.g. [0...20] (last: 5, before: "cursor:20") -> [cursor:15, cursor:16, cursor:17, cursor:18, cursor:19]
-  if (args.last) {
+  if (typeof args.last === "number") {
     if (args.before) {
       const offset = parseInt(args.before, 10);
       cursorIndex = offset - args.last + index;
@@ -1010,7 +1010,7 @@ function defaultValidateArgs(
   args: Record<string, any> = {},
   info: GraphQLResolveInfo
 ) {
-  if (!args.first && !args.last) {
+  if (!(args.first || args.first === 0) && !(args.last || args.last === 0)) {
     throw new Error(
       `The ${info.parentType}.${info.fieldName} connection field requires a "first" or "last" argument`
     );

tests/plugins/connectionPlugin.spec.ts

@@ -347,6 +347,50 @@ describe("connectionPlugin", () => {
       });
     });
 
+    it("default arg validation: allows first to be zero", async () => {
+      const schema = testConnectionSchema({});
+      const result = await execute({
+        schema,
+        document: UsersFieldFirst,
+        variableValues: { first: 0 },
+      });
+      expect(result).toEqual({
+        data: {
+          users: {
+            edges: [],
+            pageInfo: {
+              endCursor: null,
+              hasNextPage: true,
+              hasPreviousPage: false,
+              startCursor: null,
+            },
+          },
+        },
+      });
+    });
+
+    it("default arg validation: allows last to be zero", async () => {
+      const schema = testConnectionSchema({});
+      const result = await execute({
+        schema,
+        document: UsersFieldLast,
+        variableValues: { last: 0 },
+      });
+      expect(result).toEqual({
+        data: {
+          users: {
+            edges: [],
+            pageInfo: {
+              endCursor: null,
+              hasNextPage: false,
+              hasPreviousPage: true,
+              startCursor: null,
+            },
+          },
+        },
+      });
+    });
+
     it("default arg validation: throws if both first & last are provided", async () => {
       const schema = testConnectionSchema({});
       const result = await execute({