Another Repeated column in mapping for entity error

use this, is work for me:

@Column(name = "candidate_id", nullable=false)
private Long candidate_id;
@ManyToOne(optional=false)
@JoinColumn(name = "candidate_id", insertable=false, updatable=false)
private Candidate candidate;

The message is clear: you have a repeated column in the mapping. That means you mapped the same database column twice. And indeed, you have:

@Column(nullable=false)
private Long customerId;

and also:

@ManyToOne(optional=false)
@JoinColumn(name="customerId",referencedColumnName="id_customer")
private Customer customer;

(and the same goes for productId/product).

You shouldn't reference other entities by their ID, but by a direct reference to the entity. Remove the customerId field, it's useless. And do the same for productId. If you want the customer ID of a sale, you just need to do this:

sale.getCustomer().getId()

If you are stuck with a legacy database where someone already placed JPA annotations on but did NOT define the relationships and you are now trying to define them for use in your code, then you might NOT be able to delete the customerId @Column since other code may directly reference it already. In that case, define the relationships as follows:

@ManyToOne(optional=false)
@JoinColumn(name="productId",referencedColumnName="id_product", insertable=false, updatable=false)
private Product product;

@ManyToOne(optional=false)
@JoinColumn(name="customerId",referencedColumnName="id_customer", insertable=false, updatable=false)
private Customer customer;

This allows you to access the relationships. However, to add/update to the relationships you will have to manipulate the foreign keys directly via their defined @Column values. It's not an ideal situation, but if you are handed this sort of situation, at least you can define the relationships so that you can use JPQL successfully.