implement method to retrieve oldest record

db_operation.py

@@ -1,4 +1,4 @@
-'''
+ '''
 Abstraction for saving data to db
 '''
 import pandas as pd
@@ -49,6 +49,25 @@ def get_most_recent_profile(type):
         df['date'] = pd.to_datetime(df['date'])
         return df
 
+def _get_oldest(table_name, ts_column='date'):
+    query = f"SELECT * FROM {table_name} WHERE {ts_column} = (SELECT MIN({ts_column}) FROM {table_name})"
+    with create_engine(db_url).connect() as conn:
+        df = pd.read_sql(query, con=conn)
+        df[ts_column] = pd.to_datetime(df[ts_column])
+        return df
+
+def get_oldest_portfolio_profile():
+    df = _get_oldest(ts.PORTFOLIO_TABLE)
+    return df
+
+def get_oldest_stocks_proce():
+    df = _get_oldest(ts.STOCKS_PRICE_TABLE, ts_column='time')
+    return df
+
+def get_oldest_benchmark_profile():
+    df = _get_oldest(ts.BENCHMARK_TABLE)
+    return df
+
 def _get_most_recent(table_name, ts_column='date'):
     '''return the most recent entry in the table'''
     query = f"SELECT * FROM {table_name} WHERE {ts_column} = (SELECT MAX({ts_column}) FROM {table_name})"
@@ -65,12 +84,10 @@ def get_all_portfolio_profile():
 
 def get_most_recent_portfolio_profile():
     df = _get_most_recent(ts.PORTFOLIO_TABLE)
-    df['date'] = pd.to_datetime(df['date'])
     return df
 
 def get_most_recent_stocks_price():
     df = _get_most_recent(ts.STOCKS_PRICE_TABLE, ts_column='time')
-    df['time'] = pd.to_datetime(df['time'])
     return df
 
 def _append_df_to_db(df, table_name, schema):