Replace BigQuery table with API job

Question

I am using the BigQuery client libraries to perform a data ETL jpb, then load data back into BigQuery.

I'd like to overwrite the destination table every time, but currently my code is appending new data to the table every time it is run. I've read the documentation on job_config, and I have used this to set parameters for queries, but I can't figure out how to set a write disposition for the query.

Here is what I have tried so far:

roc_df = pd.DataFrame(roc_score)

job_config.write_disposition = bigquery.WriteDisposition.WRITE_TRUNCATE

dataset_ref = client.dataset('Customers')
table_ref = dataset_ref.table('propensity_scores_test')

client.load_table_from_dataframe(roc_df, table_ref, job_config=job_config).result()

And I also tried this format:

query_config = bigquery.QueryJobConfig(
    query_parameters=[
        bigquery.job.WriteDisposition('WRITE_TRUNCATE')
    ]
)

But both are currently returning the error:

BadRequest: 400 POST https://www.googleapis.com/upload/bigquery/v2/projects/my_project/jobs?uploadType=resumable: Required parameter is missing

Hoe can I write my data out and replace the table each time?

Answer 1

The load_table_from_dataframe method uses a LoadJobConfig. Here's a working snippet of code:

from google.cloud import bigquery
import pandas as pd

roc_df = pd.DataFrame([{"firstName": "Foo", "lastName": "Bar"}])

client = bigquery.Client()

dataset_ref = client.dataset('my_dataset')
table_ref = dataset_ref.table('my_table')

job_config = bigquery.job.LoadJobConfig()
job_config.write_disposition = bigquery.WriteDisposition.WRITE_TRUNCATE

client.load_table_from_dataframe(roc_df, table_ref, job_config=job_config)

The only change with your code would be:

job_config = bigquery.job.LoadJobConfig()