Assigning a DataArray with different shape to Dataset variable does not update the variable

What happened?

I encountered an issue when trying to assign a new DataArray to an existing variable in an xarray Dataset. The assignment appears to not update the variable as expected.

Here is a minimal example that reproduces the problem:

What did you expect to happen?

After the assignment, dataSet['open']should have the same data and coordinates as dataArray_new, i.e., shape (3,3) with codes ['000123', '000456', '000111'].

Minimal Complete Verifiable Example

import xarray as xr
import numpy as np


DataTime=[20260102,20260103,20260104]
codes = ['000123', '000456']

dataArray = xr.DataArray(
    np.random.randn(len(DataTime), len(codes)),
    dims=['time', 'code'],
    coords={'code': codes,'time': DataTime}
)
dataArray_new = xr.DataArray(
    np.random.randn(len(DataTime), 3),
    dims=['time', 'code'],
    coords={'code': ['000123', '000456','000111'],'time': DataTime}
)


dataSet = xr.Dataset({'open': dataArray})
dataSet['open']=dataArray_new
print(dataSet['open'])
print()
print(dataArray_new)
print("xarray version",xr.__version__)

Steps to reproduce

No response

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

output:
Python 3.13.7 (tags/v3.13.7:bcee1c3, Aug 14 2025, 14:15:11) [MSC v.1944 64 bit (AMD64)] on win32
Enter "help" below or click "Help" above for more information.

= RESTART: C:/Users/Administrator/AppData/Local/Programs/Python/Python313/delok.py
<xarray.DataArray 'open' (time: 3, code: 2)> Size: 48B
array([[ 0.00311068, -1.68021968],
[ 0.23174369, 1.72308605],
[ 0.05651745, -0.07747445]])
Coordinates:

time (time) int64 24B 20260102 20260103 20260104
code (code) <U6 48B '000123' '000456'
<xarray.DataArray (time: 3, code: 3)> Size: 72B
array([[ 0.00311068, -1.68021968, -1.19742281],
[ 0.23174369, 1.72308605, -1.11061083],
[ 0.05651745, -0.07747445, 0.70037003]])
Coordinates:

time (time) int64 24B 20260102 20260103 20260104
code (code) <U6 72B '000123' '000456' '000111'
xarray version 2026.1.0

Anything else we need to know?

No response

Environment

Start by running the minimal Python example with xarray and numpy to confirm how Dataset variable assignment handles the differing code dimension. Locate the Dataset assignment tests or implementation, add a regression case for the new shape and coordinates, and verify that dataSet['open'] matches dataArray_new after assignment.