Insert initial letter rates.

Create letter rates dao.
Query to fetch letter rates.

app/dao/letter_rate_dao.py

@@ -0,0 +1,23 @@
+from app import db
+from app.dao.dao_utils import transactional
+from app.models import LetterRate
+
+
+@transactional
+def dao_create_letter_rate(letter_rate):
+    db.session.add(letter_rate)
+
+
+def get_letter_rates_for_daterange(date, crown, sheet_count, post_class='second'):
+    rates = LetterRate.query.filter(
+        LetterRate.start_date <= date
+    ).filter((LetterRate.end_date == None) |  # noqa
+             (LetterRate.end_date > date)
+             ).filter(
+        LetterRate.crown == crown
+    ).filter(
+        LetterRate.sheet_count == sheet_count
+    ).filter(
+        LetterRate.post_class == post_class
+    ).all()
+    return rates

app/models.py

@@ -1487,7 +1487,7 @@ class LetterRate(db.Model):
     id = db.Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
     start_date = db.Column(db.DateTime, nullable=False)
     end_date = db.Column(db.DateTime, nullable=True)
-    sheet_total = db.Column(db.Integer, nullable=False)  # double sided sheet
+    sheet_count = db.Column(db.Integer, nullable=False)  # double sided sheet
     rate = db.Column(db.Numeric(), nullable=False)
     crown = db.Column(db.Boolean, nullable=False)
     post_class = db.Column(db.String, nullable=False)