CRS set on Dataset does not persist for DataArrays obtained by selecting data variable  #356

Code Sample

da1 = xr.DataArray(np.arange(10*10).reshape(10, 10), [("x", np.linspace(70,80,10)), ("y", np.linspace(20,30,10))], name='var_1')
da2 = xr.DataArray(np.arange(10*10).reshape(10, 10), [("x", np.linspace(70,80,10)), ("y", np.linspace(20,30,10))], name='var_2')

ds = xr.merge([da1,da2])

ds = ds.rio.set_crs('epsg:4326')

print('Dataset CRS: {}'.format(ds.rio.crs))
print('DataArray 1 CRS: {}'.format(ds['var_1'].rio.crs))
print('DataArray 2 CRS: {}'.format(ds['var_2'].rio.crs))

Problem description

The CRS set on a Dataset using .rio.set_crs() does not persist to a DataArray obtained by selecting individual variables from the Dataset. Printing the CRS of the Dataset gives the previously set CRS, but printing the CRS of the DataArray gives None.

Expected Output

The CRS set on a Dataset should also apply to DataArrays of individual variables. Printing DataArray.rio.crs should give the set CRS, EPSG:4326 in this case.

Environment Information

rioxarray (0.1.1) deps:
  rasterio: 1.1.0
    xarray: 0.16.2
      GDAL: 3.0.2

Other python deps:
     scipy: 1.4.1
    pyproj: 2.6.0

System:
   python: 3.7.7 (default, Mar 23 2020, 22:36:06)  [GCC 7.3.0]
   machine: Linux-5.4.89+-x86_64-with-debian-bullseye-sid

Installation method

PyPi