Fix: YearMonth 값 String으로 변환

src/main/java/mejai/mejaigg/global/jpa/YearMonthDateAttributeConverter.java

@@ -0,0 +1,25 @@
+package mejai.mejaigg.global.jpa;
+
+import java.time.YearMonth;
+import java.time.format.DateTimeFormatter;
+
+import jakarta.persistence.AttributeConverter;
+import jakarta.persistence.Converter;
+
+@Converter(autoApply = true)
+public class YearMonthDateAttributeConverter implements
+	AttributeConverter<YearMonth, String> {
+	private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM");
+
+	@Override
+	public String convertToDatabaseColumn(
+		YearMonth attribute) {
+		return attribute != null ? attribute.format(FORMATTER) : null;
+	}
+
+	@Override
+	public YearMonth convertToEntityAttribute(
+		String dbData) {
+		return dbData != null ? YearMonth.parse(dbData, FORMATTER) : null;
+	}
+}