Spark Dynamic overwrite to bigquery overwrites entire table

[jayasreej]

Hi 

I'm trying to overwrite a specific partition date(dt) data from bigquery through spark but it overwrites the entire table data.Can someone help me on this.

Spark configurations: 
"spark.sql.sources.partitionOverwriteMode" : "dynamic",

df.write.mode("overwrite") \
.format("bigquery") \
.option("partitionField","dt")\
.option("spark.sql.sources.partitionOverwriteMode","dynamic")\
.option("temporaryGcsBucket", "xxxx")\
.option("table", "project.dataset.table")\
.save()

It overwrites the entire content, can someone help me out on