Merge pull request #3 from UniExeterRSE/iss2-field-ordering

Issue 2: field ordering

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "csv-db"
-version = "0.1.0.rc3"
+version = "0.1.0.rc4"
 description = 'A Python package for working with a simple databse backed by a csv file.'
 readme = "README.md"
 requires-python = ">=3.9"

src/csv_db/core.py

@@ -48,35 +48,39 @@ class CsvDB(object):
 
     def __init__(self, path: Path, fields: Collection[str]):
         self._path = pathlib.Path(path)
-        self._fields = fields
         self._fields_arg = "fields"  # should match the name of the argument in __init__
-        self._validate_fields()
+        self._fields = self._make_fields(fields)
 
-    def _validate_fields(self) -> None:
-        """Perform checks on the supplied fields and, if present, those in the csv file.
+    def _make_fields(self, fields: Collection[str]) -> None:
+        """Make the fields to store reference in database operations.
+
+        Along the way, this method performs checks on the supplied fields and, if present,
+        those in the csv file. The checks performed are:
 
-        Checks that:
         * The collection of field names is not empty.
         * None of the field names are missing, i.e. the empty string.
         * None of the field names are repeated.
         * The supplied fields agree with those in the csv file, if the latter is present.
+
+        If all relevant checks pass, then the fields as ordered in the csv file are
+        returned. Otherwise, the supplied `fields` are returned.
         """
 
-        if len(self._fields) == 0:
+        if len(fields) == 0:
             raise ValueError(
                 f"Argument '{self._fields_arg}' defines an empty collection."
             )
 
-        if self._any_missing(self._fields):
+        if self._any_missing(fields):
             raise ValueError(f"Argument '{self._fields_arg}' contains empty field names.")
 
-        if repeated_fields := self._make_repetitions_str(self._fields):
+        if repeated_fields := self._make_repetitions_str(fields):
             raise ValueError(
                 f"Argument '{self._fields_arg}' contains repeated fields: {repeated_fields}."
             )
 
         if not self._path.exists():
-            return
+            return fields
 
         with open(self._path, mode="r") as csvfile:
             file_fields = tuple(csvfile.readline().strip().split(","))
@@ -91,11 +95,13 @@ def _validate_fields(self) -> None:
                 f"Database file {self._path} contains repeated fields: {repeated_fields}."
             )
 
-        if not set(self._fields) == set(file_fields):
+        if not set(fields) == set(file_fields):
             raise FieldsMismatchError(
                 f"'{self._fields_arg}' does not agree with the fields defined in {self._path}."
             )
 
+        return file_fields
+
     @staticmethod
     def _any_missing(coll: Collection[str]) -> bool:
         """Returns ``True`` if the empty string is in the collection `coll`."""

tests/test_core.py

@@ -269,6 +269,16 @@ def test_retrieve_missing_field_error(self):
         ):
             self.db2.retrieve(field, "1")
 
+    def test_retrieve_field_order_in_file_differs_to_instantiation(self):
+        """Test that a record can be correctly retrieved when it belongs to a csv file
+        where the order of fields differs from that given at instantiation of a new
+        database."""
+
+        write_csv_row(self.path3, ["1", "a"], mode="a")
+        self.assertEqual(
+            {self.pkey: "1", self.col1: "a"}, self.dbrev.retrieve(self.pkey, "1")
+        )
+
     def test_update_replaces_correct_record(self):
         """Test that the record with the specified field value gets updated and no other
         records get updated."""