介绍一学一做视频网站吗策划公司一般怎么收费

添加：save(对象)

删除：delete（主键或者带有主键的对象）

修改：save（对象）

对象中没有id，执行添加操作

对象中有id

id不存在：执行添加

id存在：

其余数据与数据库中一致，只发送查询

其余数据与数据库中不一致，发送更新语句

查询

查询某一个findOne（主键） 及时加载

查询某一个getOne(主键) 懒加载

使用过程中会报no session问题，需要追加@Transactional

查询某一个findOne（动态参数）

@Test
public void find() {Specification<User> spec = new Specification<User>() {@Overridepublic Predicate toPredicate(Root<User> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder cb) {Path<Object> username = root.get("username");Path<Object> id = root.get("id");Path<Object> age = root.get("age");Predicate p1 = cb.equal(username, 1111);Predicate p2 = cb.equal(id, 1);Predicate p3 = cb.equal(age, 18);Predicate[] ps = new Predicate[3];ps[0] = p1;ps[1] = p2;ps[2] = p3;Predicate predicate = cb.and(ps);return predicate;}};User user = userDao.findOne(spec);System.out.println(user);
}

查询所有findAll（）

查询所有并排序findAll（sort）

Sort sort = new Sort(Sort.Direction.DESC,"id");
List<User> userList = userdao.findAll(sort);

查询所有并分页findAll（pageable）

Pageable pageable = new PageRequest(0,5);
Page<User> page = userdao.findAll(pageable);

动态查询所有并分页findAll（动态参数,pageable）

参考查询某一个findOne（动态参数）

动态查询所有并排序findAll（动态参数,sort）

参考查询某一个findOne（动态参数）

通过JPQL语句个性化查询

//通过用户名查询
@Query("from User where username=?1")
User test01(String username);
//通过用户名、密码登录
@Query("from User where username=?1 and password = ?2")
User login(String username,String password);
//通过id搜索用户名
@Query("select username from User where id=?1")
User test02(int id);

通过SQL个性化查询

@Query(value = "select username from User where id=?1",nativeQuery = true)
User test03(int id);

通过个性化方法名称査询 find+By+属性名称+And+....

User findByUsernameAndPassword(string username,string password);
List<User> findTop5ByUsername(string username);
User findByUsernameLike(string username):

关联关系

 一对多

从多查一:默认及时加载，发送一条 sql 语句

从一査多:默认懒加载，发送多条sql语句，报错

解决方式一:追加@Transactional

解决方式二:开启及时加载

package com.xszx.beans;import javax.persistence.*;@Entity
@Table(name = "t_user")
public class User {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private int id;private String username;private String password;private int age;/*** @ManyToOne 多对一* 属性targetEntity：对方的字节码* @JoinColumn 加入列名* 属性name：列的名称* 属性referencedColumnName：对方表的主键列名*/@ManyToOne(targetEntity = Group.class)@JoinColumn(name = "gid",referencedColumnName = "gid")private Group group;public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}public User() {}public User(int id, String username, String password, int age) {this.id = id;this.username = username;this.password = password;this.age = age;}public User(int age, String password, String username) {this.age = age;this.password = password;this.username = username;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public int getId() {return id;}public void setId(int id) {this.id = id;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +'}';}
}

package com.xszx.beans;import javax.persistence.*;
import java.util.List;
@Entity
@Table(name = "t_group")
public class Group {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private int gid;private String gname;/***  @OneToMany 一对多*  属性targetEntity：对方字节码*  属性mappedBy：对方实体类中，对方属性名，关系由对方维护*  属性fetch：配置懒加载与及时加载*  */@OneToMany(targetEntity = User.class,mappedBy = "group",fetch = FetchType.EAGER)private List<User> users;public List<User> getUsers() {return users;}public void setUsers(List<User> users) {this.users = users;}public Group() {}public Group(int gid, String gname) {this.gid = gid;this.gname = gname;}public int getGid() {return gid;}public void setGid(int gid) {this.gid = gid;}public String getGname() {return gname;}public void setGname(String gname) {this.gname = gname;}@Overridepublic String toString() {return "Group{" +"gid=" + gid +", gname='" + gname + '\'' +'}';}
}

多对多

package com.xszx.beans;import javax.persistence.*;
import java.util.List;@Entity
@Table(name = "t_student")
public class Student {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private int sid;private String sname;/*** @ManyToMany 多对多* 属性targetEntity：对方的字节码* @joinTable 加入中间表* 属性name：中间表名* 属性joinColumns：本类在中间表的字段* 属性inverseJoinColumns：对方在中间表的字段*/@ManyToMany(targetEntity = Teacher.class)@JoinTable(name = "t_stu_tea",joinColumns = {@JoinColumn(name = "sid",referencedColumnName = "sid")},inverseJoinColumns = {@JoinColumn(name = "tid",referencedColumnName = "tid")})private List<Teacher> teachers;public List<Teacher> getTeachers() {return teachers;}public void setTeachers(List<Teacher> teachers) {this.teachers = teachers;}public Student() {}public Student(int sid, String sname) {this.sid = sid;this.sname = sname;}public int getSid() {return sid;}public void setSid(int sid) {this.sid = sid;}public String getSname() {return sname;}public void setSname(String sname) {this.sname = sname;}@Overridepublic String toString() {return "Student{" +"sid=" + sid +", sname='" + sname + '\'' +'}';}
}

package com.xszx.beans;import javax.persistence.*;
import java.util.List;@Entity
@Table(name = "t_teacher")
public class Teacher {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private int tid;private String tname;@ManyToMany(targetEntity = Student.class,mappedBy = "teachers")private List<Student> students;public Teacher() {}public Teacher(int tid, String tname) {this.tid = tid;this.tname = tname;}public List<Student> getStudents() {return students;}public void setStudents(List<Student> students) {this.students = students;}public int getTid() {return tid;}public void setTid(int tid) {this.tid = tid;}public String getTname() {return tname;}public void setTname(String tname) {this.tname = tname;}@Overridepublic String toString() {return "Teacher{" +"tid=" + tid +", tname='" + tname + '\'' +'}';}
}