Switch to blanking tombstoned data with null, not empty string.

This accomplishes two things:

* It removes the need for an additional `channel_name_reservation` table, since `channel.name` now only contains non-null values for active channels, and
* It nicely dovetails with the idea that `null` means an unknown value in SQL-land.

2 files changed, 15 insertions, 40 deletions

diff --git a/src/channel/app.rs b/src/channel/app.rs
index 0409076..75c662d 100644
--- a/src/channel/app.rs
+++ b/src/channel/app.rs
@@ -23,9 +23,9 @@ impl<'a> Channels<'a> {
     pub async fn create(&self, name: &str, created_at: &DateTime) -> Result<Channel, CreateError> {
         let mut tx = self.db.begin().await?;
         let created = tx.sequence().next(created_at).await?;
-        let channel = tx.channels().create(name, &created).await?;
-        tx.channels()
-            .reserve_name(&channel, name)
+        let channel = tx
+            .channels()
+            .create(name, &created)
             .await
             .duplicate(|| CreateError::DuplicateName(name.into()))?;
         tx.commit().await?;
diff --git a/src/channel/repo.rs b/src/channel/repo.rs
index 4b10c54..1cd1c80 100644
--- a/src/channel/repo.rs
+++ b/src/channel/repo.rs
@@ -28,7 +28,7 @@ impl<'c> Channels<'c> {
                 values ($1, $2, $3, $4)
                 returning
                     id as "id: Id",
-                    name,
+                    name as "name!", -- known non-null as we just set it
                     created_at as "created_at: DateTime",
                     created_sequence as "created_sequence: Sequence"
             "#,
@@ -52,22 +52,6 @@ impl<'c> Channels<'c> {
         Ok(channel)
     }
 
-    pub async fn reserve_name(&mut self, channel: &History, name: &str) -> Result<(), sqlx::Error> {
-        let channel = channel.id();
-        sqlx::query!(
-            r#"
-                insert into channel_name_reservation (id, name)
-                values ($1, $2)
-            "#,
-            channel,
-            name,
-        )
-        .execute(&mut *self.0)
-        .await?;
-
-        Ok(())
-    }
-
     pub async fn by_id(&mut self, channel: &Id) -> Result<History, sqlx::Error> {
         let channel = sqlx::query!(
             r#"
@@ -76,8 +60,8 @@ impl<'c> Channels<'c> {
                     channel.name,
                     channel.created_at as "created_at: DateTime",
                     channel.created_sequence as "created_sequence: Sequence",
-                    deleted.deleted_at as "deleted_at: DateTime",
-                    deleted.deleted_sequence as "deleted_sequence: Sequence"
+                    deleted.deleted_at as "deleted_at?: DateTime",
+                    deleted.deleted_sequence as "deleted_sequence?: Sequence"
                 from channel
                 left join channel_deleted as deleted
                     using (id)
@@ -88,7 +72,7 @@ impl<'c> Channels<'c> {
         .map(|row| History {
             channel: Channel {
                 id: row.id,
-                name: row.name,
+                name: row.name.unwrap_or_default(),
                 deleted_at: row.deleted_at,
             },
             created: Instant::new(row.created_at, row.created_sequence),
@@ -121,7 +105,7 @@ impl<'c> Channels<'c> {
         .map(|row| History {
             channel: Channel {
                 id: row.id,
-                name: row.name,
+                name: row.name.unwrap_or_default(),
                 deleted_at: row.deleted_at,
             },
             created: Instant::new(row.created_at, row.created_sequence),
@@ -156,7 +140,7 @@ impl<'c> Channels<'c> {
         .map(|row| History {
             channel: Channel {
                 id: row.id,
-                name: row.name,
+                name: row.name.unwrap_or_default(),
                 deleted_at: row.deleted_at,
             },
             created: Instant::new(row.created_at, row.created_sequence),
@@ -176,17 +160,6 @@ impl<'c> Channels<'c> {
         let id = channel.id();
         sqlx::query_scalar!(
             r#"
-                delete from channel_name_reservation
-                where id = $1
-                returning 1 as "deleted: bool"
-            "#,
-            id,
-        )
-        .fetch_one(&mut *self.0)
-        .await?;
-
-        sqlx::query_scalar!(
-            r#"
                 insert into channel_deleted (id, deleted_at, deleted_sequence)
                 values ($1, $2, $3)
                 returning 1 as "deleted: bool"
@@ -202,10 +175,12 @@ impl<'c> Channels<'c> {
         // retconned to have been the empty string. Someone reading the event stream
         // afterwards, or looking at channels via the API, cannot retrieve the
         // "deleted" channel's information by ignoring the deletion event.
+        //
+        // This also avoids the need for a separate name reservation table to ensure that live channels have unique names, since the `channel` table's name field is unique over non-null values.
         sqlx::query_scalar!(
             r#"
                 update channel
-                set name = ""
+                set name = null
                 where id = $1
                 returning 1 as "updated: bool"
             "#,
@@ -261,8 +236,8 @@ impl<'c> Channels<'c> {
                     channel.name,
                     channel.created_at as "created_at: DateTime",
                     channel.created_sequence as "created_sequence: Sequence",
-                    deleted.deleted_at as "deleted_at: DateTime",
-                    deleted.deleted_sequence as "deleted_sequence: Sequence"
+                    deleted.deleted_at as "deleted_at?: DateTime",
+                    deleted.deleted_sequence as "deleted_sequence?: Sequence"
                 from channel
                 left join channel_deleted as deleted
                     using (id)
@@ -276,7 +251,7 @@ impl<'c> Channels<'c> {
         .map(|row| History {
             channel: Channel {
                 id: row.id,
-                name: row.name,
+                name: row.name.unwrap_or_default(),
                 deleted_at: row.deleted_at,
             },
             created: Instant::new(row.created_at, row.created_sequence),