Spring JDBC and Hibernate

Question 1

Which class is used to fetch JDBC connections from database?

Answer 1

DataSource class is used.

Question 2

Which are minimum required configurations for creating a database connection?

Answer 2

Driveclassname,
URL,
username,
password

Question 3

Which class of DBCP is used to create and pool database connection?

Answer 3

BasicDataSource

Question 4

Which tag is used to read properties file?

Answer 4

context:property-placeholder and its location property is used to define path of file.

Question 5

Which utility is provided in spring that helps in reading data from database or ORM tools?

Answer 5

JDBCTemplate, HibernateTemplate are available which do the heavylifting of cleaning up resources.

Question 6

Which methods are used to fetch data and execute DML instructions?

Answer 6

To get the data queryXXXmethods are used and for inserting, updating and deleting execute() method is used.

Question 7

Which overloaded methods are used for querying different data types of single row and multiple rows

Answer 7

queryForInt
queryForObject
queryForList
queryForMap
queryForRowSet

Question 8

What does queryForMap return?

Answer 8

queryForMap returns single row in a Map map.

Question 9

Why should bind variables be used in place of appending to prepare query?

Answer 9

Preparing query manually makes it prone to SQL injection. So bind variables are used.

Question 10

Using bind variables with JDBC template

Answer 10

JDBC template takes extra parameter Object[] for passing arguments.
jdbcTemplate.queryForObject("Select * from Students where id=?", new Object[] {id}, new StudentMapper());

Question 11

Which interface is used to map from row to domain objects?

Answer 11

RowMapper interface is used to convert from row to domain object. mapRow(ResultSet rs) should be implemented.

Question 12

Which method is used for inserting, updating and deleting rows from table using jdbc template?

Answer 12

update() method is used to execute these statements and int returned represents the number of rows affected.

Question 13

Which template variant can be used to create statement using names?

Answer 13

NamedParameterJdbcTemplate can be used.
String sql = "insert into students (NAME) values (:name)";
Map params = new HashMap<>();
params.put("name", name);
jdbcTemplate.update(sql, params);

Question 14

How to use SQL batch operations using JDBC template?

Answer 14

SqlParameterSource[] params = SqlParameterSourceUtils.createBatch(employees.toArray());
jdbcTemplate.batchUpdate(“query”, params);

Question 15

Which interface is provided to set batch values to prepare statement and fire batch operation in jdbctemplate

Answer 15

BatchPreparedStatementSetter is provided. It has method that gives you prepared statement and index that you can use to fetch value at that index and set that in prepared statement. The batching logic is implemented by the template.

Question 16

What is advantage of ORM framework.

Answer 16

1) It hides the underlying database and so we can change that in future without change in application.
2) Makes integration with database easy by automatically converting beans and relations to sql query.
3) Reduces development time.

Question 17

In which ways can mapping for class to column name be provided? Including id field, etc?

Answer 17

XML or by annotation.

Question 18

How to provide hibernate mapping configuration using xml file

Answer 18

hibernate mappings are usually called class.hbm.xml format. 
class name="classname" table = "courses
    id name = "id"
    generator class="assigned"
    id over
    property name="name"
    property name="price"

Question 19

Which things are needed to start hibernate integration with spring?

Answer 19

1) Datasource bean BasicDataSource
2) A session factory - LocalSessionFactoryBean. Provide datasource as dependency and provide all hibernate configuration files.
3) hibernate properties - which includes dialect (database specific), hbm2ddl.auto to convert from hibernate to DDL queries, show sql which will print the sql created by hibernate

Question 20

Should Hibernate template be used for Spring JPA integration??

Answer 20

Using EntityManager class is recommended instead of HibernateTemplate.

Question 21

How to get list of objects from HibernateTemplate?

Answer 21

return hibernateTemplate.executeFind(new HibernateCallback>() {

		public List doInHibernate(Session session) throws HibernateException, SQLException {
			return session.createCriteria(Course.class).setMaxResults(100).list();
		}
	});

Question 22

How to inject EntityManager inside a bean where it is needed?

Answer 22

@PersistenceContext annoatation can be used to inject EntityManager into a class.

Question 23

Is EntityManager an interface or class?

Answer 23

It is an interface. All communication happens through EntityManager.

Question 24

Which method is used to find an object using some property like id?

Answer 24

entityManager.find(Person.class, id);

Question 25

Which method is used to insert of update an entity using EntityManager?

Answer 25

entityManager.merge(person);

Question 26

Which method is used to delete somthing using EntityManager?

Answer 26

If you have to delete by id and you don’t have person object, then you first have to query person object using entityManager.findById(id) and then use that person object to get it deleted.
entityManager.remove(person) is used to delete.

Question 27

How to find list of all records of particular type using EntityManager. Similar to Select * From Person table?

Answer 27

First we will have to create a TypedQuery and then use it to gget all results.

TypedQuery query = entityManager.createNamedQuery(“find_all_persons”, Person.class);
List persons = query.getResultList();

Question 28

EntityManager is part of which JSR?

Answer 28

It is part of JPA (Java Persistence API) JSR.

Question 29

What is TypedQuery?

Answer 29

TypedQuery gives you option of specifying the type of entity when creating the query. So there is no need for explicit cast. Whereas normal Query requires type cast from Object to required type.

Question 30

What is entityManager.createNamedQuery()

Answer 30

Similar to how constatns is defined. Named query is way to define it by giving it a namw. You can define the query either in hibernate configuration xml or using annotation on the entity class.

Question 31

How to define NamedQuery in entity class?

Answer 31

@NamedQuery(name=”find_all_persos”, query = “select p from Person p”)

The query is an HQL query.

Question 32

How to automatically fire sql DDLs and DMLs when spring boot data applications starts?

Answer 32

Keeping a file named data.sql is automatically picked up from classpath and is fired by spring.

Question 33

Why is “data.sql” file useful in Spring boot data application?

Answer 33

It is useful to initialize database with some initial data.

Question 34

Provide different types of queries that can be made using Hibernate?

Answer 34

Native Query - This query is SQL query that can be directly executed on database using database client.

entityManager.createNativeQuery(“”) can be used to create it.

NamedQuery - Similar to constant, queries can be provided names and defined in either hibernate configuration file or on entity class using annotation. When creating query just name of query needs to be provided to EntityManager.

Query q = entityManager.createNamedQuery(“name”);

TypedQuery - Usually query returns objects but typed query gives you option to provide entity type, so you don’t need to explicitly cast the result.

TypedQuery tq = entityManager.createNamedQuery(“name”, Person.class);