Merge 3 Tables into 1 SpringBoot + Postgres - postgresql

Question

I have an Application written in spring boot with 3 Tables T1, T2 and T3 on Postgres
t1 one2many mapping with t2 and t2 one2many with t3
How can I merge these tables into one? Do the model and repository still stay the same?
Model for T1
#Entity
#Table(name = "maintenance_type")
#EntityListeners(AuditingEntityListener.class)
#JsonIgnoreProperties(value = { "createdAt", "updatedAt" }, allowGetters = true)
public class MaintenanceType implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#NotBlank
#Column(unique=true)
private String changeType;
#Column(nullable = false, updatable = false)
#Temporal(TemporalType.TIMESTAMP)
#CreatedDate
private Date createdAt;
#Column(nullable = false)
#Temporal(TemporalType.TIMESTAMP)
#LastModifiedDate
private Date updatedAt;
#OneToMany(mappedBy = "maintenanceType", cascade = CascadeType.ALL)
private Set<TierTwoQuestion> tierTwoQuestion;
public MaintenanceType() {
}
public MaintenanceType(Long id, String changeType) {
super();
this.id = id;
this.changeType = changeType;
}
public MaintenanceType(String changeType) {
super();
this.changeType = changeType;
}
public Set<TierTwoQuestion> getTierTwoQuestion() {
return tierTwoQuestion;
}
//
public void setTierTwoQuestion(Set<TierTwoQuestion> tierTwoQuestion) {
this.tierTwoQuestion = tierTwoQuestion;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getChangeType() {
return changeType;
}
public void setChangeType(String changeType) {
this.changeType = changeType;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
public Date getUpdatedAt() {
return updatedAt;
}
public void setUpdatedAt(Date updatedAt) {
this.updatedAt = updatedAt;
}
}
Model for T2
#Entity
#Table(name = "tier_two_question")
#EntityListeners(AuditingEntityListener.class)
#JsonIgnoreProperties(value = { "createdAt", "updatedAt" }, allowGetters = true)
public class TierTwoQuestion implements Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#NotBlank
#Column(unique=true)
private String question;
#ManyToOne
#JoinColumn(name = "maintenanceId", nullable = false)
private MaintenanceType maintenanceType;
#OneToMany(mappedBy = "tierTwoQuestion", cascade = CascadeType.ALL)
private Set<TierThreeQuestion> tierThreeQuestion;
#Column(nullable = false, updatable = false)
#Temporal(TemporalType.TIMESTAMP)
#CreatedDate
private Date createdAt;
#Column(nullable = false)
#Temporal(TemporalType.TIMESTAMP)
#LastModifiedDate
private Date updatedAt;
public TierTwoQuestion() {
}
public TierTwoQuestion(Long id) {
super();
this.id = id;
this.question = question;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getQuestion() {
return question;
}
public void setQuestion(String question) {
this.question = question;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
public Date getUpdatedAt() {
return updatedAt;
}
public void setUpdatedAt(Date updatedAt) {
this.updatedAt = updatedAt;
}
// public MaintenanceType getMaintenanceType() {
// return maintenanceType;
// }
public void setMaintenanceType(MaintenanceType maintenanceType) {
this.maintenanceType = maintenanceType;
}
public Set<TierThreeQuestion> getTierThreeQuestion() {
return tierThreeQuestion;
}
public void setTierThreeQuestion(Set<TierThreeQuestion> tierThreeQuestion) {
this.tierThreeQuestion = tierThreeQuestion;
}
}
I tried adding recreating the model with all T1 T2 T3 in one table but not working as expected