![\"\"](\"https:\/\/coding101.xyz\/wp-content\/uploads\/2023\/12\/image.png\")
<\/figure>\n\n\n\nNote a couple of things:<\/p>\n\n\n\n
- \n
- One to many first -> second<\/li>\n\n\n\n
- The field in the second table that links to the first is first_id<\/li>\n\n\n\n
- There is a foreign key constraint from second to the first<\/li>\n<\/ul>\n\n\n\n
OK, now the application. Here are the maven dependencies (basically just add spring-java-jpa and that is it)<\/p>\n\n\n\n
1\n 2\n 3\n 4\n 5\n 6\n 7\n 8\n 9\n10\n11\n12\n13\n14\n15\n16\n17\n18<\/pre><\/td>
<dependencies><\/span>\n <dependency><\/span>\n <groupId><\/span>org.springframework.boot<\/groupId><\/span>\n <!-- for starting with web, use starter-web --><\/span>\n <artifactId><\/span>spring-boot-starter<\/artifactId><\/span>\n <\/dependency><\/span>\n <dependency><\/span>\n <groupId><\/span>org.springframework.boot<\/groupId><\/span>\n <!-- for starting with web, use starter-web --><\/span>\n <artifactId><\/span>spring-boot-starter-data-jpa<\/artifactId><\/span>\n <\/dependency><\/span>\n <!-- https:\/\/mvnrepository.com\/artifact\/org.mariadb.jdbc\/mariadb-java-client --><\/span>\n <dependency><\/span>\n <groupId><\/span>org.mariadb.jdbc<\/groupId><\/span>\n <artifactId><\/span>mariadb-java-client<\/artifactId><\/span>\n <version><\/span>3.1.4<\/version><\/span>\n <\/dependency><\/span>\n <\/dependencies><\/span>\n<\/pre><\/td><\/tr><\/table><\/div>\n\n\n\nThe entity classes are FirstDt and SecondDt, and here they are: <\/p>\n\n\n\n
1\n 2\n 3\n 4\n 5\n 6\n 7\n 8\n 9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n22\n23\n24\n25\n26\n27\n28\n29\n30\n31\n32\n33\n34\n35\n36\n37\n38\n39\n40\n41\n42\n43\n44\n45\n46\n47\n48\n49\n50\n51\n52\n53\n54\n55\n56\n57\n58\n59\n60\n61\n62\n63\n64\n65<\/pre><\/td>
package<\/span> org.example<\/span>.dt<\/span>;\n\nimport<\/span> jakarta.persistence.*;\n\nimport<\/span> java.util.ArrayList;\nimport<\/span> java.util.List;\n\n@Entity\n@Table(name = "first"<\/span>)\n@NamedQueries(\n {@NamedQuery(name="first.query"<\/span>, query="select a from FirstDt a where a.comments = :cm1"<\/span>)}\n)\npublic<\/span> class<\/span> FirstDt {\n @Id\n @Column(name = "first_id"<\/span>)\n private<\/span> String id;\n\n @Column(name = "first_coments"<\/span>)\n private<\/span> String comments;\n\n @Column(name = "shoe_size"<\/span>)\n private<\/span> int<\/span> shoeSize;\n\n @OneToMany(fetch = FetchType.LAZY<\/span>)\n @JoinColumn(name = "first_id"<\/span>)\n private<\/span> final<\/span> List<SecondDt> items;\n\n public<\/span> FirstDt() {\n this<\/span>.items<\/span> = new<\/span> ArrayList<>();\n }\n\n public<\/span> String getId() {\n return<\/span> id;\n }\n\n public<\/span> void<\/span> setId(String id) {\n this<\/span>.id<\/span> = id;\n }\n\n public<\/span> String getComments() {\n return<\/span> comments;\n }\n\n public<\/span> void<\/span> setComments(String comments) {\n this<\/span>.comments<\/span> = comments;\n }\n\n public<\/span> int<\/span> getShoeSize() {\n return<\/span> shoeSize;\n }\n\n public<\/span> void<\/span> setShoeSize(int<\/span> shoeSize) {\n this<\/span>.shoeSize<\/span> = shoeSize;\n }\n\n @Override\n public<\/span> String toString() {\n final<\/span> StringBuilder sb = new<\/span> StringBuilder("FirstDt{"<\/span>);\n sb.append<\/span>("id='"<\/span>).append<\/span>(id).append<\/span>('\\''<\/span>);\n sb.append<\/span>(", comments='"<\/span>).append<\/span>(comments).append<\/span>('\\''<\/span>);\n sb.append<\/span>(", shoeSize="<\/span>).append<\/span>(shoeSize);\n sb.append<\/span>('}'<\/span>);\n return<\/span> sb.toString<\/span>();\n }\n}\n<\/pre><\/td><\/tr><\/table><\/div>\n\n\n\nAnd second dt is here:<\/p>\n\n\n\n
1\n 2\n 3\n 4\n 5\n 6\n 7\n 8\n 9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n22\n23\n24\n25\n26\n27\n28\n29\n30\n31\n32\n33\n34\n35\n36\n37\n38\n39\n40\n41\n42\n43\n44\n45\n46\n47\n48<\/pre><\/td>
package<\/span> org.example<\/span>.dt<\/span>;\n\nimport<\/span> jakarta.persistence.Column;\nimport<\/span> jakarta.persistence.Entity;\nimport<\/span> jakarta.persistence.Id;\nimport<\/span> jakarta.persistence.Table;\n\n@Entity\n@Table(name = "second"<\/span>)\npublic<\/span> class<\/span> SecondDt {\n\n @Id\n @Column(name = "second_id"<\/span>)\n private<\/span> String id;\n\n @Column(name = "second_info"<\/span>)\n private<\/span> String info;\n\n @Column(name = "salary"<\/span>)\n private<\/span> double<\/span> salary;\n\n public<\/span> SecondDt() {\n }\n\n public<\/span> String getId() {\n return<\/span> id;\n }\n\n public<\/span> void<\/span> setId(String id) {\n this<\/span>.id<\/span> = id;\n }\n\n public<\/span> String getInfo() {\n return<\/span> info;\n }\n\n public<\/span> void<\/span> setInfo(String info) {\n this<\/span>.info<\/span> = info;\n }\n\n public<\/span> double<\/span> getSalary() {\n return<\/span> salary;\n }\n\n public<\/span> void<\/span> setSalary(double<\/span> salary) {\n this<\/span>.salary<\/span> = salary;\n }\n}\n<\/pre><\/td><\/tr><\/table><\/div>\n\n\n\nAnd this is the service that is used to access through those<\/p>\n\n\n\n
1\n 2\n 3\n 4\n 5\n 6\n 7\n 8\n 9\n 10\n 11\n 12\n 13\n 14\n 15\n 16\n 17\n 18\n 19\n 20\n 21\n 22\n 23\n 24\n 25\n 26\n 27\n 28\n 29\n 30\n 31\n 32\n 33\n 34\n 35\n 36\n 37\n 38\n 39\n 40\n 41\n 42\n 43\n 44\n 45\n 46\n 47\n 48\n 49\n 50\n 51\n 52\n 53\n 54\n 55\n 56\n 57\n 58\n 59\n 60\n 61\n 62\n 63\n 64\n 65\n 66\n 67\n 68\n 69\n 70\n 71\n 72\n 73\n 74\n 75\n 76\n 77\n 78\n 79\n 80\n 81\n 82\n 83\n 84\n 85\n 86\n 87\n 88\n 89\n 90\n 91\n 92\n 93\n 94\n 95\n 96\n 97\n 98\n 99\n100\n101\n102\n103\n104\n105\n106\n107\n108<\/pre><\/td>
package<\/span> org.example<\/span>.service<\/span>;\n\nimport<\/span> jakarta.persistence.EntityManager;\nimport<\/span> jakarta.persistence.PersistenceContext;\nimport<\/span> jakarta.persistence.Query;\nimport<\/span> jakarta.persistence.TypedQuery;\nimport<\/span> jakarta.transaction.Transactional;\nimport<\/span> org.example.dt.FirstDt;\nimport<\/span> org.example.persist.IFirstRepo;\nimport<\/span> org.springframework.beans.factory.annotation.Autowired;\nimport<\/span> org.springframework.data.domain.Sort;\nimport<\/span> org.springframework.stereotype.Component;\n\nimport<\/span> java.util.List;\n\n@Component\npublic<\/span> class<\/span> InfoService {\n\n @PersistenceContext\n private<\/span> EntityManager em;\n\n @Autowired\n private<\/span> IFirstRepo firstRepo;\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> String createFirst() throws<\/span> Exception {\n FirstDt first = new<\/span> FirstDt();\n first.setId<\/span>("id4"<\/span>);\n first.setComments<\/span>("the comments for id4"<\/span>);\n first.setShoeSize<\/span>(25<\/span>);\n\n em.persist<\/span>(first);\n\n return<\/span> "current"<\/span>;\n }\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> List<FirstDt> getAllFirst() {\n List<FirstDt> items = firstRepo.findAll<\/span>();\n\n return<\/span> items;\n }\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> List<FirstDt> getAllSorted() {\n List<FirstDt> items = firstRepo.findAll<\/span>(Sort.by<\/span>(Sort.Direction<\/span>.DESC<\/span>, "shoeSize"<\/span>).and<\/span>(Sort.by<\/span>(Sort.Direction<\/span>.ASC<\/span>, "comments"<\/span>)));\n\n return<\/span> items;\n }\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> List<FirstDt> getThatOne(String id) {\n return<\/span> firstRepo.getThatOne<\/span>(id);\n }\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> double<\/span> getShoeSum() {\n return<\/span> firstRepo.getSum<\/span>();\n }\n\n @Transactional(Transactional.TxType<\/span>.REQUIRED<\/span>)\n public<\/span> double<\/span> getNativeShoeSum() {\n return<\/span> firstRepo.getNativeSum<\/span>();\n }\n\n public<\/span> FirstDt searchThatFirst() {\n TypedQuery<FirstDt> query = em.createQuery<\/span>("select a from FirstDt a where a.id = :itemId"<\/span>, FirstDt.class<\/span>);\n query.setParameter<\/span>("itemId"<\/span>, "id1"<\/span>);\n List<FirstDt> items = query.getResultList<\/span>();\n\n FirstDt res = null<\/span>;\n if<\/span> (items.size<\/span>() > 0<\/span>) {\n res = items.get<\/span>(0<\/span>);\n }\n\n return<\/span> res;\n }\n\n public<\/span> FirstDt searchId() {\n FirstDt res = null<\/span>;\n\n TypedQuery<FirstDt> query = em.createNamedQuery<\/span>("first.query"<\/span>, FirstDt.class<\/span>);\n query.setParameter<\/span>("cm1"<\/span>, "the comments for id2"<\/span>);\n List<FirstDt> items = query.getResultList<\/span>();\n\n