Select MAX timestamp with JPA2 Criteria API

问题:

So my entity has:

@Column(name="TS", nullable=false)
private java.sql.Timestamp timestamp; 

My generated MetaModel has:

public static volatile SingularAttribute<MyEntity,Timestamp> timestamp;

I want to select by the Max Timestamp value:

Root<MyEntity> root = query.from(MyEntity.class);
Expression maxExpression = cb.max(root.get(MyEntity_.timestamp));

But I am not allowed because:

max(Expression<N> x) Create an aggregate expression applying the numerical max operation. <N extends java.lang.Number> Expression

Of course Timestamp does not extend Number.

How can I do a MAX on a Timestamp column using the typesafe Criteria API ?

回答1:

Instead of max you have to use CriteriaBuilder.greatest for Timestamp (and for Date, String and other Comparables as well). And if you ever need MIN for Timestamp, then use least method instead

Similar kind of issue can be be faced with less/greater/equal comparisons. Firs one accepts argument that extends Number, second one is for other comparables:

• lt vs. lessThan
• le vs. lessThanOrEqualTo
• ge vs. greaterThanOrEqualTo
• gt vs. greaterThan