move database utils to Database/Utils, create DatabaseMigrator

PluralKit.Core/Database/Utils/UpdateQueryBuilder.cs

@@ -0,0 +1,45 @@
+using System.Text;
+
+using Dapper;
+
+namespace PluralKit.Core
+{
+    public class UpdateQueryBuilder
+    {
+        private readonly QueryBuilder _qb;
+        private readonly DynamicParameters _params = new DynamicParameters();
+
+        private UpdateQueryBuilder(QueryBuilder qb)
+        {
+            _qb = qb;
+        }
+        
+        public static UpdateQueryBuilder Insert(string table) => new UpdateQueryBuilder(QueryBuilder.Insert(table));
+        public static UpdateQueryBuilder Update(string table, string condition) => new UpdateQueryBuilder(QueryBuilder.Update(table, condition));
+        public static UpdateQueryBuilder Upsert(string table, string conflictField) => new UpdateQueryBuilder(QueryBuilder.Upsert(table, conflictField));
+
+        public UpdateQueryBuilder WithConstant<T>(string name, T value)
+        {
+            _params.Add(name, value);
+            _qb.Constant(name, $"@{name}");
+            return this;
+        }
+
+        public UpdateQueryBuilder With<T>(string columnName, T value)
+        {
+            _params.Add(columnName, value);
+            _qb.Variable(columnName, $"@{columnName}");
+            return this;
+        }
+
+        public UpdateQueryBuilder With<T>(string columnName, Partial<T> partialValue)
+        {
+            return partialValue.IsPresent ? With(columnName, partialValue.Value) : this;
+        }
+
+        public (string Query, DynamicParameters Parameters) Build(string suffix = "")
+        {
+            return (_qb.Build(suffix), _params);
+        }
+    }
+}