Added donation errors

ref #66

src/errors/DonationErrors.ts

@@ -0,0 +1,25 @@
+import { IsString } from 'class-validator';
+import { NotAcceptableError, NotFoundError } from 'routing-controllers';
+
+/**
+ * Error to throw when a Donation couldn't be found.
+ */
+export class DonationNotFoundError extends NotFoundError {
+	@IsString()
+	name = "DonationNotFoundError"
+
+	@IsString()
+	message = "Donation not found!"
+}
+
+/**
+ * Error to throw when two Donations' ids don't match.
+ * Usually occurs when a user tries to change a Donation's id.
+ */
+export class DonationIdsNotMatchingError extends NotAcceptableError {
+	@IsString()
+	name = "DonationIdsNotMatchingError"
+
+	@IsString()
+	message = "The ids don't match! \n And if you wanted to change a Donation's id: This isn't allowed!"
+}