feat: cache Discord DM channels in database

PluralKit.Core/Database/Migrations/26.sql

@@ -0,0 +1,12 @@
+-- schema version 26
+-- cache Discord DM channels in the database
+
+alter table accounts alter column system drop not null;
+alter table accounts drop constraint accounts_system_fkey;
+alter table accounts
+    add constraint accounts_system_fkey
+    foreign key (system) references systems(id) on delete set null;
+
+alter table accounts add column dm_channel bigint;
+
+update info set schema_version = 26;

PluralKit.Core/Database/Repository/ModelRepository.Account.cs

@@ -1,9 +1,14 @@
+using Dapper;
+
 using SqlKata;
 
 namespace PluralKit.Core;
 
 public partial class ModelRepository
 {
+    public async Task<ulong?> GetDmChannel(ulong id)
+        => await _db.Execute(c => c.QueryFirstOrDefaultAsync<ulong?>("select dm_channel from accounts where uid = @id", new { id = id }));
+
     public async Task UpdateAccount(ulong id, AccountPatch patch)
     {
         _logger.Information("Updated account {accountId}: {@AccountPatch}", id, patch);

PluralKit.Core/Database/Repository/ModelRepository.System.cs

@@ -24,7 +24,8 @@ public partial class ModelRepository
         var query = new Query("accounts")
             .Select("systems.*")
             .LeftJoin("systems", "systems.id", "accounts.system")
-            .Where("uid", accountId);
+            .Where("uid", accountId)
+            .WhereNotNull("system");
         return _db.QueryFirst<PKSystem?>(query);
     }
 
@@ -111,10 +112,13 @@ public partial class ModelRepository
         // We have "on conflict do nothing" since linking an account when it's already linked to the same system is idempotent
         // This is used in import/export, although the pk;link command checks for this case beforehand
 
+        // update 2022-01: the accounts table is now independent of systems
+        // we MUST check for the presence of a system before inserting, or it will move the new account to the current system
+
         var query = new Query("accounts").AsInsert(new { system, uid = accountId });
+        await _db.ExecuteQuery(conn, query, "on conflict (uid) do update set system = @p0");
 
         _logger.Information("Linked account {UserId} to {SystemId}", accountId, system);
-        await _db.ExecuteQuery(conn, query, "on conflict do nothing");
 
         _ = _dispatch.Dispatch(system, new UpdateDispatchData
         {
@@ -125,7 +129,10 @@ public partial class ModelRepository
 
     public async Task RemoveAccount(SystemId system, ulong accountId)
     {
-        var query = new Query("accounts").AsDelete().Where("uid", accountId).Where("system", system);
+        var query = new Query("accounts").AsUpdate(new
+        {
+            system = (ulong?)null
+        }).Where("uid", accountId).Where("system", system);
         await _db.ExecuteQuery(query);
         _logger.Information("Unlinked account {UserId} from {SystemId}", accountId, system);
         _ = _dispatch.Dispatch(system, new UpdateDispatchData

PluralKit.Core/Database/Utils/DatabaseMigrator.cs

@@ -9,7 +9,7 @@ namespace PluralKit.Core;
 internal class DatabaseMigrator
 {
     private const string RootPath = "PluralKit.Core.Database"; // "resource path" root for SQL files
-    private const int TargetSchemaVersion = 25;
+    private const int TargetSchemaVersion = 26;
     private readonly ILogger _logger;
 
     public DatabaseMigrator(ILogger logger)