added post object

amanuensis/backend/post.py

@@ -0,0 +1,42 @@
+"""
+Post query interface
+"""
+
+import re
+
+from sqlalchemy import select, func
+
+from amanuensis.db import DbContext, Post
+from amanuensis.errors import ArgumentError
+
+def create(
+    db: DbContext,
+    lexicon_id: int,
+    user_id: int,
+    body: str) -> Post:
+    """
+    Create a new post
+    """
+
+    # Verify lexicon id
+    if not isinstance(lexicon_id, int):
+        raise ArgumentError('Lexicon id must be an integer.')
+    
+    # Verify user_id
+    if not isinstance(user_id, int):
+        raise ArgumentError('Lexicon id must ne an integer.')
+
+    # Verify body
+    if not isinstance(body, str):
+        raise ArgumentError('Post body must be a string.')
+    if not body.strip():
+        raise ArgumentError('Post body cannot be empty.')
+
+    new_post = Post(
+        lexicon_id=lexicon_id,
+        user_id=user_id,
+        body=body
+    )
+    db.session.add(new_post)
+    db.session.commit()
+    return new_post