Case-insensitive JPA unique constraint?

问题

I'm currently using

@Entity
public class ... {

    /**
     * @return the loginName
     */
    @Column(unique=true)
    public String getLoginName() {
        return loginName;
    }

but like to have a case-insensitive constraint such that a login name "UPPERCASE" is not allowed when there is already a login name "uppercase" in the database. Is there anything I can use or do I have to create the dirty workaround of storing a lower case version in a separate column?

回答1:

This is not something covered by JPA, and I'd say not even implementations (e.g. Hibernate).

One thing you can do is create a @PrePersist and @PreUpdate handler that will fill another (additional) entity field with normalized (lowercase) value, and have the constraint on that.

@Entity Foo { 
    private value;
    @Column(unique = true)
    private valueLowercased;

    @PrePersist @PreUpdate private prepare(){
        this.valueLowercased = value == null ? null : value.toLowerCase();
    }
}

Non-JPA approach could be to have an additional column myColumnLowercased with an UNIQUE INDEX and a trigger that would set the value to LOWERCASE(new.myColumn). (Nomenclature may differ across databases.)

Some databases support "functional indexes" which is you can index by an expression.

CREATE INDEX test1_lower_col1_idx ON test1 (lower(col1));

来源：https://stackoverflow.com/questions/22645618/case-insensitive-jpa-unique-constraint