Function test_to_sql

dask/dataframe/io/tests/test_sql.py:484–557

(npartitions, parallel)

@pytest.mark.parametrize("npartitions", (1, 2))
@pytest.mark.parametrize("parallel", (False, True))
def test_to_sql(npartitions, parallel):
    df_by_age = df.set_index("age")
    df_appended = pd.concat(
        [
            df,
            df,
        ]
    )

    ddf = dd.from_pandas(df, npartitions)
    ddf_by_age = ddf.set_index("age")

    # Simple round trip test: use existing "number" index_col
    with tmp_db_uri() as uri:
        ddf.to_sql("test", uri, parallel=parallel)
        result = read_sql_table("test", uri, "number")
        assert_eq(df, result)

    # Test writing no index, and reading back in with one of the other columns as index (`read_sql_table` requires
    # an index_col)
    with tmp_db_uri() as uri:
        ddf.to_sql("test", uri, parallel=parallel, index=False)

        result = read_sql_table("test", uri, "negish")
        assert_eq(df.set_index("negish"), result)

        result = read_sql_table("test", uri, "age")
        assert_eq(df_by_age, result)

    # Index by "age" instead
    with tmp_db_uri() as uri:
        ddf_by_age.to_sql("test", uri, parallel=parallel)
        result = read_sql_table("test", uri, "age")
        assert_eq(df_by_age, result)

    if PANDAS_GE_300:
        string_dtype = "str"
    else:
        string_dtype = "object"

    # Index column can't have "object" dtype if no partitions are provided
    with tmp_db_uri() as uri:
        ddf.set_index("name").to_sql("test", uri)
        with pytest.raises(
            TypeError,
            match=f'Provided index column is of type "{string_dtype}".  If divisions is not provided the index column type must be numeric or datetime.',
        ):
            read_sql_table("test", uri, "name")

    # Test various "if_exists" values
    with tmp_db_uri() as uri:
        ddf.to_sql("test", uri)

        # Writing a table that already exists fails
        with pytest.raises(ValueError, match="Table 'test' already exists"):
            ddf.to_sql("test", uri)

        ddf.to_sql("test", uri, parallel=parallel, if_exists="append")