I'm designing a Java report application that can receive any SQL query(on a already defined database) and then I display the result in a table grid in a Vue.js application.
I have some doubts on how to load a Java generic/hybrid class that can fit differents SQL queries.
I mean, is it possible to create a class in Java that can change/mutate during runtime so I can map different SQL queries in it?
I know that it is possible to use the java.sql.ResultSetMetaData to get the column name, table name, column class name, etc. (I don't know if it possible with hibernate)
But I don't know how to map the results in a unique class.
For example:
I have 3 differents queries and they could be a lot more:
1) SELECT ID, COUNTRY_NAME FROM COUNTRY;
2) SELECT CODE, NAME, PRICE FROM PRODUCT;
3) SELECT P.CODE, P.NAME, S.NAME
FROM PRODUCT P
JOIN SUPPLIER S
ON S.ID = P.SUPPLIER_ID
WHERE P.PRICE > 25;
I need to map this query results(one at a time obviously) in a generic class so then I pass it to the Vue app to display it in a grid.
Is it a way to do that?
Don't reinvent the wheel and use what is already available and what is well tested.
What you're looking for is called Spring JDBC, or, for an even higher level, Java Persistence API.
Using Spring JDBC to extract a set of records might look like
final List<YourClass> results =
jdbcTemplate.queryForList(
"Native SQL statement",
queryArguments,
YourClass.class
);
Using a JPA implementation (e.g. Hibernate, EclipseLink, ObjectDb), the operation might look like
final TypedQuery<YourClass> query = entityManager.createQuery("JPQL statement", YourClass.class);
final List<YourClass> results = query.getResultList();
Related
I want to get all the values from a particular column in JPA and store all values into a list. currently, I am using the below approach but I am getting records in something else format.can someone please help me out
Query q1 = factory.createNativeQuery("select * from booking_attendee where booking_id="+id);
List<String> em1=q1.getResultList();
return em1;
query otput
em=[[Ljava.lang.Object;#68606667, [Ljava.lang.Object;#2cd7f99a, [Ljava.lang.Object;#137a5a5, [Ljava.lang.Object;#a45cc1c, [Ljava.lang.Object;#61fdc06d, [Ljava.lang.Object;#72f5eee1, [Ljava.lang.Object;#4e536797]
If you want to create a native query for this, it is more about how to solve this in SQL. You do not say SELECT * which means all columns. You would have to say SELECT your_column_name to select only a specific column.
Query q1 = factory.createNativeQuery("SELECT your_column FROM booking_attendee");
List<String> em1 = q1.getResultList();
The WHERE clause could and should be defined with the parameter binding of JPA. There are several advantages concerning performance and SQL injection.
Named parameter binding is special to the persistence provider (e.g. Hibernate). The common way for JPA is using ? to let your code be portable to other providers.
Query q1 = factory.createNativeQuery("SELECT your_column FROM booking_attendee b WHERE b.booking_id = ?");
q1.setParameter(1, id);
List<String> em1 = q1.getResultList();
Native queries offer the possibilities to use original SQL. Like this, some features which are specific for your database could be used with this. Nevertheless, if you do not have very specific SQL code, you should also have a look in JPQL, the specific query language of JPA, and the JPA Criteria API which offers advantages when you want to refactor your code, shows errors during compile time and makes the dynamic creation of queries easier.
In Hibernate, you can use the 'SELECT' queries in native SQL like this :
Query query = session.createSQLQuery("SELECT ... FROM ...");
But I would want to use an 'INSERT' query.
So, I looked at the documentation, and it seems you must go directly to the mapped class and write the code inside it.
But I would want to use it as I do for a 'SELECT' query (outside the mapped class) since it looks much more pratical.
Indeed, why would the treatment be different between 'SELECT' and 'INSERT' for a hibernate native SQL query ?
An HQL INSERT cannot be used to directly insert arbitrary entities—it can only be used to insert entities constructed from information obtained from SELECT queries (unlike ordinary SQL, in which an INSERT command can be used to insert arbitrary data into a table, as well as insert values selected from other tables).
Here’s the syntax of the INSERT statement:
INSERT INTO path ( property [, ...]) select
The name of an entity is path. The property names are the names of properties of entities listed in the FROM path of the incorporated SELECT query. The select query is an HQL SELECT query (as described in the next section).
As this HQL statement can only use data provided by an HQL select, its application can be limited. An example of copying users to a purged table before actually purging them might look like this:
Query query=session.createQuery("insert into purged_accounts(id, code, status) "+
"select id, code, status from acount where status=:status");
query.setString("status", "purged");
int rowsCopied=query.executeUpdate();
Or you can use
session.persist(obj);
where obj is the object of the POJO class let say TestClass
TestClass obj=new TestClass('','',''); //paramatrized constructor for the values you want to insert in your database.
Is possible to remove a clause (the order by clause in my case) from a dynamically constructed query in jOOQ.
Suppose that after creating the query:
DSLContext create = DSL.using(SQLDialect.POSTGRES);
SelectQuery<Record> query = create.select().from("myTable").where("fk = 1").orderBy(DSL.field("pk")).getQuery();
System.out.println(query.getSQL());
// select * from myTable where (fk = 1) order by pk asc
I want to change the order by clause or remove it to get only
select * from myTable where (fk = 1)
Is possible make this with jOOQ?. If is not possible and anyone knows a query builder library that allows this will be also welcome.
This currently cannot be done through the public API. In a future jOOQ 4.0, there might be a cleaner separation of the DSL API and the Model API, where such a model API would allow you to freely manipulate all your query parts, including removing objects again from SELECT clauses.
Right now, you have at least two options to implement dynamic SQL:
Don't add the ORDER BY clause until you know whether you need it:
SelectQuery<?> select = create
.select()
.from("myTable")
.where("fk = 1")
.getQuery();
if (someCondition)
select.addOrderBy(DSL.field("pk"));
Alternative piece of logic:
List<SortField<?>> orderBy = new ArrayList<>();
if (someCondition)
orderBy.add(DSL.field("pk").asc());
create.select()
.from("myTable")
.where("fk = 1")
.orderBy(orderBy);
Post-process / transform your query using an ExecuteListener or a VisitListener. This is more of a workaround in edge-cases, though.
In your particular case, you should probably go with option 1. Another, more functional approach to tackling dynamic SQL generation is documented here.
I have a named query as below;
#NamedQuery(name = "MyEntityClass.findSomething", query = "SELECT item FROM MyTable mytbl")
Now I want to append dynamic sort clause to this query (based on UI parameters)
Can I get an example using JPQL for doing the same (like how to set a dynamic ORDER BY in the Entity class)
I have already tried using CriteriaQuery, but was looking for a JPQL implementation now.
NamedQueries are by definition NOT dynamic, it is not correct to change them programmatically.
So the way to go is to create a JPQL query (but not a named query) like this:
TypedQuery<MyEntity> query = em.createdQuery("SELECT item FROM MyEntity item ORDER BY "+sortingCol, MyEntity.class);
On the other hand, if you REALLY want to use the named query, you could do that the following way:
#NamedQuery(name = "MyEntityClass.findSomething", query = MyEntity.NAMED_QUERY)
#Entity
public class MyEntity {
public static final NAMED_QUERY= "SELECT item FROM MyTable mytbl";
//+your persistent fields/properties...
}
//and later in your code
TypedQuery<MyEntity> query = entityManager.createQuery(MyEntity.NAMED_QUERY + " ORDER BY " + sortingCol, MyEntity.class);
Complementing for JPA 2.1
As of JPA 2.1 it is possible to define named queries programmatically.
This can be achieved using entityManagerFactory.addNamedQuery(String name, Query).
Example:
Query q = this.em.createQuery("SELECT a FROM Book b JOIN b.authors a WHERE b.title LIKE :title GROUP BY a");
this.em.getEntityManagerFactory().addNamedQuery("selectAuthorOfBook", q);
// then use like any namedQuery
Reference here
This can be useful, for instance, if you have the orderby field defined as a application parameter. So, when the application starts up or on the first run of the query, you could define the NamedQuery with the defined OrderBy field.
On the other side, if your OrderBy can be changed anytime (or changes a lot), then you need dynamic queries instead of NamedQuery (static). It would not worth to (re)create a NamedQuery every time (by performance).
#NamedQuery
Persistence Provider converts the named queries from JPQL to SQL at deployment time.
Until now, there is no feature to create/update the query with #NamedQuery annotation at runtime.
On the other hand, you can use Reflection API, to change the annotation value at runtime. I think It is not solution, also it is not you wanted .
em.createQuery()
Persistence Provider converts the dynamic queries from JPQL to SQL every time it is invoked.
The main advantage of using dynamic queries is that the query can be created based on the user inputs.
I need to set a table name dynamically so that I use query.setText(tname,abc)
e.g: select a.name from :tname where a.id = '2'
I used setText() because when I use setString() it says "tname is a invalid parameter" because I assume that Hibernate adds '' when setting string parameters.
But even setText() does not help and gives the same exception.
How can I set the table name dynamically?
Reply to PSR:
So you mean replace table name as a java string replacement. But then we can not take support of sql injections prevention etc from hibernate right? Also How we bind parameters in hibernate in a situation where like statement,
Eg: name like "%:name%"
This also gives me Illegal argument exception: Parameter does not exist as a named parameter when i try to bind it using query.setString(name,"def");
Hibernate will not do this for you, because it works with PreparedStatements, and you can't prepare a statement where the table being queried isn't known yet.
I don't see why you would be exposing table names to end users, so preventing SQL injection doing a regular string substitution should be easy. You use some sort of business logic to determine the correct table from a list that only you know. The table name isn't coming from user input at all.
Depending on your choice of RDBMS, you may find a discriminator column, or table inheritance with partitioning to be a better way of handling a situation where identical queries are made against different tables.
It is not possible to set table name dynamically.You can set dynamically column names.it is not possible to set table name
try like this
select a.name from '+table name+'where a.id = '2'
In my opinion, There are 2 ways to resolve this issue:
1- If you are using Spring and Hibernate together, you could use SpEL and it would be like #{#entityName} as it is described here
#Entity
public class User {
#Id
#GeneratedValue
Long id;
String lastname;
}
public interface UserRepository extends JpaRepository<User,Long> {
#Query("select u from #{#entityName} u where u.lastname = ?1")
List<User> findByLastname(String lastname);
}
2-You could use CriteriaBuilder like
CriteriaQuery<YourEntity> cr = cb.createQuery(YourEntity.class);
Root<YourEntity> root = cr.from(YourEntity.class);
cr.select(root);
I copied the source codes from the provided links and they are described there much better