问题
May I know how to convert the following MySQL SQL to JPA query?
SELECT * FROM ORDER
WHERE LPAD(BATCH, 2, ' ') < LPAD('X', 2, ' ') ;
What I couldn't figure out is the LPAD() string function in JPA.
Do you have any idea?
回答1:
I know that is a very old post, but i am always be questioned by some colleagues when they are building JPA queries how to do the same thing. Almost never you will find a perfect fit function to do what do you want. But, using some logic you can get the same result, in full JPA.
A example of LPAD.
Expression<String> numberWithZeroLeft = builder.concat("0000", root.get("myNumber")); //Return something like 000012
Expression<Integer> expressionLength = builder.length(numberWithZeroLeft);
Expression<String> numberLpad = builder.substring(numberWithZeroLeft, e.builder.sum(expressionLength, -3), e.builder.literal(4)); //Return something like 0012
query.select(numberLpad);
Think in something like:
I have a string X, and need a string formatted in 4 zeros.
So we will get 0000 + X => "0000X"
And now just get the 4 last characters using substring.
I hope that help someone.
Cheers. =]
回答2:
In EclipseLink 2.1 there is a function FUNC for calling database specific functions, for example:
FUNC('LPAD', BATCH, 2, ' ') < FUNC('LPAD', 'X', 2, ' ')
From EclipseLink 2.4 and JPA 2.1 there is FUNCTION operator with the same functionality
来源：https://stackoverflow.com/questions/16040562/mysqls-lpad-string-function-in-jpa-query