Refactor member updates to use a patch object

PluralKit.Core/Utils/UpdateQueryBuilder.cs

@@ -0,0 +1,51 @@
+using System.Text;
+
+using Dapper;
+
+namespace PluralKit.Core
+{
+    public class UpdateQueryBuilder
+    {
+        private readonly string _table;
+        private readonly string _condition;
+        private readonly DynamicParameters _params = new DynamicParameters();
+
+        private bool _hasFields = false;
+        private readonly StringBuilder _setClause = new StringBuilder();
+
+        public UpdateQueryBuilder(string table, string condition)
+        {
+            _table = table;
+            _condition = condition;
+        }
+
+        public UpdateQueryBuilder WithConstant<T>(string name, T value)
+        {
+            _params.Add(name, value);
+            return this;
+        }
+
+        public UpdateQueryBuilder With<T>(string columnName, T value)
+        {
+            _params.Add(columnName, value);
+
+            if (_hasFields)
+                _setClause.Append(", ");
+            else _hasFields = true;
+
+            _setClause.Append($"{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 append = "")
+        {
+            var query = $"update {_table} set {_setClause} where {_condition} {append}";
+            return (query, _params);
+        }
+    }
+}