Make euph_trees a temporary database

src/vault/migrate.rs

@@ -60,13 +60,6 @@ fn m1(tx: &mut Transaction) -> rusqlite::Result<()> {
             CHECK (start IS NULL OR end IS NOT NULL)
         ) STRICT;
 
-        CREATE TABLE euph_trees (
-            room TEXT NOT NULL,
-            id INT NOT NULL,
-
-            PRIMARY KEY (room, id)
-        );
-
         CREATE INDEX euph_idx_msgs_room_id_parent
         ON euph_msgs (room, id, parent);
 

src/vault/prepare.rs

@@ -0,0 +1,29 @@
+use rusqlite::Connection;
+
+pub fn prepare(conn: &mut Connection) -> rusqlite::Result<()> {
+    conn.execute_batch(
+        "
+        CREATE TEMPORARY TABLE euph_trees (
+            room TEXT NOT NULL,
+            id INT NOT NULL,
+
+            PRIMARY KEY (room, id)
+        ) STRICT;
+
+        INSERT INTO euph_trees (room, id)
+        SELECT room, id
+        FROM euph_msgs
+        WHERE parent IS NULL
+        UNION
+        SELECT room, parent
+        FROM euph_msgs
+        WHERE parent IS NOT NULL
+        AND NOT EXISTS(
+            SELECT *
+            FROM euph_msgs AS parents
+            WHERE parents.room = euph_msgs.room
+            AND parents.id = euph_msgs.parent
+        );
+        ",
+    )
+}