Core sampler

The core sampler can now retrieve data from the database and output it in a syntax Postgres can understand, in the order Postgres needs.

apps/cli/utilities/core_sampler/core_sampler/core_sampler.py

@@ -9,6 +9,7 @@ The core sampler outputs an SQL file you can use to load the core sample into a
 
 import argparse
 from typing import Any, Iterable
+import datetime
 
 import psycopg2 as pg
 import psycopg2.extras as extras
@@ -54,7 +55,7 @@ class MDDBConnector:
 
 
 class RowWriter:
-    def write_row(self, table: str, row: dict):
+    def write_rows(self, table: str, row: dict):
         raise NotImplementedError
 
 
@@ -106,8 +107,24 @@ class CoreSampler(RowWriter):
         """
         rows.write_to(self)
 
-    def write_row(self, table: str, row: dict):
-        pass  # print((table, row))
+    def write_rows(self, table: str, rows: list[dict]):
+        columns = rows[0].keys()
+        print(f"COPY {table} ({', '.join(columns)}) FROM stdin;")
+        for row in rows:
+            print("\t".join([self.copy_format(row[col]) for col in columns]))
+        print("\.")
+
+    def copy_format(self, value):
+        if value == None:
+            return "\\N"
+        elif isinstance(value, str):
+            return value
+        elif isinstance(value, int) or isinstance(value, float):
+            return str(value)
+        elif isinstance(value, datetime.date):
+            return value.isoformat()
+        else:
+            raise TypeError(f"Unable to figure out what to do with {value} of type {type(value)}")
 
 
 class Table:
@@ -163,7 +180,7 @@ class Table:
         :param columns: columns to consider in the generated WHERE clause
         :return: RowSet for the rows in this table
         """
-
+        # print(f"Fetching from {self.name} according to {','.join(columns)}")
         # 1. Escape the WHERE clause entries. it's important to use the primary keys
         #    to retrieve the values from the previous resultset; the new columns will
         #    appear in the query below.
@@ -243,8 +260,7 @@ class RowSet:
         return self.table.relations()
 
     def write_to(self, writer: RowWriter):
-        for row in self.rows:
-            writer.write_row(self.table.name, row)
+        writer.write_rows(self.table.name, self.rows)
 
     def __iter__(self):
         return iter(self.rows)