In JPA, the query is:
Query q = entityManager.createQuery("select o from Product o WHERE o.category = :value");
q.setParameter("category", category);
How can I set category to any category in JPA? So if the null category passed, I simple ignore the category parameter, select all products.
JPQL WHERE Clause. The WHERE clause of a query consists of a conditional expression used to select objects or values that satisfy the expression. The WHERE clause restricts the result of a select statement or the scope of an update or delete operation.
Let's follow the Spring Data JPA naming convention to write a query method for the IN clause for the Product entity class. Example: Consider the Product entity class and if we want to retrieve products with In clause then here is the Spring data JPA query method: List<Product> findByNameIn(List<String> names);
The JpaSpecificationExecutor<T> interface declares the methods that can be used to invoke database queries that use the JPA Criteria API. This interface has one type parameter T that describes the type of the queried entity.
In order to define SQL to execute for a Spring Data repository method, we can annotate the method with the @Query annotation — its value attribute contains the JPQL or SQL to execute. The @Query annotation takes precedence over named queries, which are annotated with @NamedQuery or defined in an orm.
How can I set category to any category in JPA? So if the null category passed, I simple ignore the category parameter, select all products.
You'll have to build the query dynamically here. With HQL (this is a simplified example):
Map<String, Object> params = new HashMap<String, Object>();
StringBuffer hql = new StringBuffer("from Product p");
boolean first = true;
if (category != null) {
hql.append(first ? " where " : " and ");
hql.append("p.category = :category");
params.put("category", category);
}
// And so on...
Query query = session.createQuery(hql.toString());
Iterator<String> iter = params.keySet().iterator();
while (iter.hasNext()) {
String name = iter.next();
Object value = params.get(name);
query.setParameter(name, value);
}
List results = query.list()
But, actually, my recommendation would be to use the Criteria API here:
Criteria criteria = session.createCriteria(Product.class);
if (category != null) {
criteria.add(Expression.eq("category", category);
}
// And so on...
List results = criteria.list();
Much simpler for complicated dynamic queries.
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