[arrow] branch master updated: ARROW-16371: [JS] Fix error iterating tables with no batches (#13287)

[domoritz]

This is an automated email from the ASF dual-hosted git repository.

domoritz pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/arrow.git


The following commit(s) were added to refs/heads/master by this push:
     new 709c1d38a3 ARROW-16371: [JS] Fix error iterating tables with no 
batches (#13287)
709c1d38a3 is described below

commit 709c1d38a3370725a10e0dd0287caecf3f6e42b3
Author: Paul Taylor <paul.e.tay...@me.com>
AuthorDate: Wed Jun 1 11:31:46 2022 -0700

    ARROW-16371: [JS] Fix error iterating tables with no batches (#13287)
    
    Authored-by: ptaylor <paul.e.tay...@me.com>
    Signed-off-by: Dominik Moritz <domor...@gmail.com>
---
 js/src/table.ts             | 5 ++++-
 js/src/vector.ts            | 2 +-
 js/test/unit/table-tests.ts | 4 ++++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/js/src/table.ts b/js/src/table.ts
index 4f7dec182f..26f77d74f5 100644
--- a/js/src/table.ts
+++ b/js/src/table.ts
@@ -224,7 +224,10 @@ export class Table<T extends TypeMap = any> {
      * Iterator for rows in this Table.
      */
     public [Symbol.iterator]() {
-        return iteratorVisitor.visit(new Vector(this.data)) as 
IterableIterator<Struct<T>['TValue']>;
+        if (this.batches.length > 0) {
+            return iteratorVisitor.visit(new Vector(this.data)) as 
IterableIterator<Struct<T>['TValue']>;
+        }
+        return (new Array(0))[Symbol.iterator]();
     }
 
     /**
diff --git a/js/src/vector.ts b/js/src/vector.ts
index a67b5527b3..362a141389 100644
--- a/js/src/vector.ts
+++ b/js/src/vector.ts
@@ -67,7 +67,7 @@ export class Vector<T extends DataType = any> {
         const data: Data<T>[] = input[0] instanceof Vector
             ? (input as Vector<T>[]).flatMap(x => x.data)
             : input as Data<T>[];
-        if (data.some((x) => !(x instanceof Data))) {
+        if (data.length === 0 || data.some((x) => !(x instanceof Data))) {
             throw new TypeError('Vector constructor expects an Array of Data 
instances.');
         }
         const type = data[0]?.type;
diff --git a/js/test/unit/table-tests.ts b/js/test/unit/table-tests.ts
index 92159c1398..50c8565f0f 100644
--- a/js/test/unit/table-tests.ts
+++ b/js/test/unit/table-tests.ts
@@ -99,6 +99,10 @@ describe(`Table`, () => {
         expect(new Table().numRows).toBe(0);
     });
 
+    test(`empty table produces an empty iterator`, () => {
+        expect([...new Table()]).toHaveLength(0);
+    });
+
     describe(`constructor`, () => {
         test(`creates an empty Table with Columns`, () => {
             let i32 = new Vector([makeData({ type: new Int32 })]);