Migration documentation and example command

src/registrar/management/commands/load_domains_data.py

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+"""Load domains from registry export."""
+
+import csv
+import logging
+import sys
+
+from django.core.management.base import BaseCommand
+from django.db.transaction import atomic
+
+from registrar.models import Domain
+
+
+logger = logging.getLogger(__name__)
+
+
+def _domain_dict_reader(file_object, **kwargs):
+    """A csv DictReader with the correct field names for escrow_domains data.
+
+    All keyword arguments are sent on to the DictReader function call.
+    """
+    # field names are from escrow_manifests without "f"
+    return csv.DictReader(
+        file_object,
+        fieldnames=[
+            "Name",
+            "Roid",
+            "IdnTableId",
+            "Registrant",
+            "ClID",
+            "CrRr",
+            "CrID",
+            "CrDate",
+            "UpRr",
+            "UpID",
+            "UpDate",
+            "ExDate",
+            "TrDate",
+        ],
+        **kwargs,
+    )
+
+
+class Command(BaseCommand):
+    help = "Load domain data from a delimited text file on stdin."
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--sep", default="|", help="Separator character for data file"
+        )
+
+    def handle(self, *args, **options):
+        separator_character = options.get("sep")
+        reader = _domain_dict_reader(sys.stdin, delimiter=separator_character)
+        # accumulate model objects so we can `bulk_create` them all at once.
+        domains = []
+        for row in reader:
+            name = row["Name"]
+            logger.info("Processing domain %s", name)
+
+            # Ensure that there is a `Domain` object for each domain name in
+            # this file and that it is active. There is a uniqueness
+            # constraint for active Domain objects, so we are going to account
+            # for that here with this check so that our later bulk_create
+            # should succeed
+            if Domain.objects.filter(name=name, is_active=True).exists():
+                # don't do anything, this domain is here and active
+                continue
+            else:
+                domains.append(Domain(name=name, is_active=True))
+        logger.info("Creating %d new domains", len(domains))
+        Domain.objects.bulk_create(domains)