Class MigrationWriter

django/db/migrations/writer.py:118–302

Take a Migration instance and is able to produce the contents of the migration file from it.

class MigrationWriter:
    """
    Take a Migration instance and is able to produce the contents
    of the migration file from it.
    """

    def __init__(self, migration, include_header=True):
        self.migration = migration
        self.include_header = include_header
        self.needs_manual_porting = False

    def as_string(self):
        """Return a string of the file contents."""
        items = {
            "replaces_str": "",
            "initial_str": "",
            "run_before_str": "",
            "atomic_str": "",
        }

        imports = set()

        # Deconstruct operations
        operations = []
        for operation in self.migration.operations:
            operation_string, operation_imports = OperationWriter(operation).serialize()
            imports.update(operation_imports)
            operations.append(operation_string)
        items["operations"] = "\n".join(operations) + "\n" if operations else ""

        # Format dependencies and write out swappable dependencies right
        dependencies = []
        for dependency in self.migration.dependencies:
            if dependency[0] == "__setting__":
                dependencies.append(
                    "        migrations.swappable_dependency(settings.%s),"
                    % dependency[1]
                )
                imports.add("from django.conf import settings")
            else:
                dependencies.append("        %s," % self.serialize(dependency)[0])
        items["dependencies"] = (
            "\n".join(sorted(dependencies)) + "\n" if dependencies else ""
        )

        # Format imports nicely, swapping imports of functions from migration
        # files for comments
        migration_imports = set()
        for line in list(imports):
            if re.match(r"^import (.*)\.\d+[^\s]*$", line):
                migration_imports.add(line.split("import")[1].strip())
                imports.remove(line)
                self.needs_manual_porting = True

        # django.db.migrations is always used, but models import may not be.
        # If models import exists, merge it with migrations import.
        if "from django.db import models" in imports:
            imports.discard("from django.db import models")