migrate to sqlalchemy-aio.

a big refactor that:

- fixes some issues that might have happened (or not) with asynchronous
    reactions to payments;
- paves the way to https://github.com/lnbits/lnbits/issues/121;
- uses more async/await notation which just looks nice; and
- makes it simple(r?) for one extension to modify stuff from other extensions.

lnbits/extensions/paywall/crud.py

@@ -1,45 +1,43 @@
 from typing import List, Optional, Union
 
-from lnbits.db import open_ext_db
 from lnbits.helpers import urlsafe_short_hash
 
+from . import db
 from .models import Paywall
 
 
-def create_paywall(
+async def create_paywall(
     *, wallet_id: str, url: str, memo: str, description: Optional[str] = None, amount: int = 0, remembers: bool = True
 ) -> Paywall:
-    with open_ext_db("paywall") as db:
-        paywall_id = urlsafe_short_hash()
-        db.execute(
-            """
-            INSERT INTO paywalls (id, wallet, url, memo, description, amount, remembers)
-            VALUES (?, ?, ?, ?, ?, ?, ?)
-            """,
-            (paywall_id, wallet_id, url, memo, description, amount, int(remembers)),
-        )
+    paywall_id = urlsafe_short_hash()
+    await db.execute(
+        """
+        INSERT INTO paywalls (id, wallet, url, memo, description, amount, remembers)
+        VALUES (?, ?, ?, ?, ?, ?, ?)
+        """,
+        (paywall_id, wallet_id, url, memo, description, amount, int(remembers)),
+    )
 
-    return get_paywall(paywall_id)
+    paywall = await get_paywall(paywall_id)
+    assert paywall, "Newly created paywall couldn't be retrieved"
+    return paywall
 
 
-def get_paywall(paywall_id: str) -> Optional[Paywall]:
-    with open_ext_db("paywall") as db:
-        row = db.fetchone("SELECT * FROM paywalls WHERE id = ?", (paywall_id,))
+async def get_paywall(paywall_id: str) -> Optional[Paywall]:
+    row = await db.fetchone("SELECT * FROM paywalls WHERE id = ?", (paywall_id,))
 
     return Paywall.from_row(row) if row else None
 
 
-def get_paywalls(wallet_ids: Union[str, List[str]]) -> List[Paywall]:
+async def get_paywalls(wallet_ids: Union[str, List[str]]) -> List[Paywall]:
     if isinstance(wallet_ids, str):
         wallet_ids = [wallet_ids]
 
-    with open_ext_db("paywall") as db:
-        q = ",".join(["?"] * len(wallet_ids))
-        rows = db.fetchall(f"SELECT * FROM paywalls WHERE wallet IN ({q})", (*wallet_ids,))
+    q = ",".join(["?"] * len(wallet_ids))
+    rows = await db.fetchall(f"SELECT * FROM paywalls WHERE wallet IN ({q})", (*wallet_ids,))
 
     return [Paywall.from_row(row) for row in rows]
 
 
-def delete_paywall(paywall_id: str) -> None:
-    with open_ext_db("paywall") as db:
-        db.execute("DELETE FROM paywalls WHERE id = ?", (paywall_id,))
+async def delete_paywall(paywall_id: str) -> None:
+    await db.execute("DELETE FROM paywalls WHERE id = ?", (paywall_id,))