[EDIT] ModelからEntityへ変換するメソッドを作成しました。

src/main/java/com/example/demo/app/domain/model/TransactionModel.java

@@ -3,7 +3,9 @@ package com.example.demo.app.domain.model;
 import java.time.LocalDate;
 import java.util.List;
 
+import com.example.demo.app.infra.entity.CategoryEntity;
 import com.example.demo.app.infra.entity.TransactionEntity;
+import com.example.demo.app.infra.entity.UserEntity;
 
 import lombok.AllArgsConstructor;
 import lombok.Getter;
@@ -35,4 +37,13 @@ public class TransactionModel {
 		return transactionEntityList.stream().map(TransactionModel::convertFrom).toList();
 	}
 	
+	public static TransactionEntity convertTo(TransactionModel transactionModel, UserEntity userEntity, CategoryEntity categoryEntity) {
+		return new TransactionEntity(
+				transactionModel.getTransactionId(),
+				userEntity,
+				categoryEntity,
+				transactionModel.getAmount(),
+				transactionModel.getTransactionDate());
+	}
+	
 }