how would you approach problem of simple app, allowing users to summarise/calculate average of price values of inventory stored? MVC model, Spring, H2. Do I need Hibernate to achieve that? How to access fields of particular items stored?
Is it a requirement to use H2? If no, just 'read' the inventory and calculate on the fly. Build the minimal solution.
If yes, I personally prefer to go with Spring Boot / Spring Data / Hibernate as this is widely used and better to maintain than a self-build solution. You could get the information with a custom query at the repository - something like:
#Query(value = "SELECT AVG(price) FROM product")
public Double getAveragePrice();
With https://bootify.io you can setup your Spring Boot app with the database model, and can add the custom logic on top.
Related
I have spring boot application with JPA and MySQL. The table is already created and data are present. From the spring boot application, we need to create two API - get a particular record using id and get all the records. I created a model class but confused with usage of #Entity. Because I'm not going to insert/delete a record from the database. I want to use only for select the record.
For Select query (findBy), do we need to use #Entity annotation at the top of model class?
Yes, you would need to use #Entity to mark your model class, this tells JPA that your class is used for mapping to and from a database table. If you want to make sure that you don't accidentally overwrite the data, you could implement a check via #EntityListener, as described in this answer.
I am using spring boot, spring data JPA, I am searching for solution to get all column names of a given table. But could not found as per my requirements
Not want a solution with native query.Looking for general solution using spring data abstraction.
I am able to get the column names using normal java but i want to fetch them using spring data JPA.
they are several ways
public interface TableMetadataRepository extends JpaRepository<TableMetadata, TableMetadataKey>
{
TableMetadata findByTableName(String tableName);
}
then you can go for
List<TableMetadata> metadata = tableMetadataRepository.findAll()
TableMetadata metadataofspecifictable = tableMetadataRepository.findByTableName("urtable");
I want to make userName property in User node as a unique.
I used below code but it doesn't create a unique constraint in the Neo4j database.
#Property(name = "name")
#Index(unique = true)
private String usreName;
FYI, I'm using the Neo4j Server version: 3.3.6 (community) With Spring Boot 2.
but if I create a constraint in the Neo4j Browser by myself, it works.
CREATE CONSTRAINT ON (user:User) ASSERT user.userName IS UNIQUE
Is there a way to force Spring Data Neo4J to create unique properties, without creating them by myself in Database?
You need to configure the auto index manager if you want the application code create the constraints.
You can find the best fitting option in the documentation:
https://docs.spring.io/spring-data/neo4j/docs/current/reference/html/#reference:indexing:creation
Just a note on this topic: Think about the auto index creation like Hibernate's DDL support. It is a helper at development time. You should not use assert and update in production environments but only validate.
Reason
In Spring Data Neo4j 4, index management concerns were removed from
the mapping framework entirely.
(from Index Management in Spring Data Neo4j)
Solution
#Autowired
private SessionFactory sessionFactory;
#PostConstruct
public void createIndexesAndConstraints() {
Session session = sessionFactory.openSession();
Result result = session.query("CREATE INDEX ON :User(userName)", Collections.EMPTY_MAP);
}
You can configure the mode our auto index manager works in through application.properties
spring.data.neo4j.auto-index=validate # or
# spring.data.neo4j.auto-index=update
# spring.data.neo4j.auto-index=assert
Default mode is none. Apart from that, what #meistermeier says applies.
Also, Neo4jOperations was deprecated in SDN 4 something and has been removed in SDN 5. Use Session instead for operations "near" the database.
Thank you #ThirstForKnowledg for your answer. But I have 3 other Questions:
1- I'm using Spring Boot 2, and I can not see Neo4jOperations in my classpath to import it.
2- Should I put this in my Entity node or in another bean?
3- What about after running my application two or more times? I think it would cause an exception for the second time or more.
How to write JPA query in Spring Data that uses at least one of three parameters?
I have these three parameters:
Id (PK)
Name
Surname
Client must supply at least one of these three parameters and I want to find user by these not-empty parameters.
Is it possible to create such custom query to my repository or do I have to create custom queries for all possible combination of WHERE conditions?
You can have your repository extend org.springframework.data.querydsl.QueryDslPredicateExecutor and use the inherited findAll(Predicate predicate) method to query using any combination of parameters.
You would not then have to write any query methods:
http://docs.spring.io/spring-data/jpa/docs/1.10.5.RELEASE/reference/html/#core.extensions.querydsl
You can also have the Predicate automatically bound in a Spring MVC Controller as detailed here:
https://spring.io/blog/2015/09/04/what-s-new-in-spring-data-release-gosling#querydsl-web-support
and here:
https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#core.web.type-safe
So your controller can then automatically handle a search with 1,2 or all 3 parameters passed as request parameters without your having to write any code at all.
This is where you need the ability to create dynamic queries at runtime.
In your application code, you should have logic to build the predicate based on whether each of the above properties from the input DTO is empty or not.
One way to do it is to use QueryDSL.
To use QueryDSL, you should include the relevant dependency in your pom/gradle file and then your repository should extend the QueryDslPredicateExecutor interface. This will give you two additional generic finder methods.
T findAll(Predicate) or
Page<T> findAll(Predicate, Pageable)
One thing to keep in mind is that the above two methods are appropriate where this is no need to do a join
Your requirement here seems to be a single table query, so either one of the finder methods should suffice.
If you do need to do a join with other tables and need fine grained control over how the JOIN happens (INNER JOIN vs LEFT OUTER JOIN vs CROSS JOIN) etc, then you should consider creating a Custom repository that your repository can extend.
And then provide your own customImpl that you can now access from the repository.
thanks a lot for the reply ... as i read Spring is not easy flexible as other framework... for i.e i tried some node js api framework and it is easier and more flexible .. what do you think about this ?
In a dao class implementation,I want to use different sql query depending upon the underlying database. Since my SQL query is complex which selects from a database view and uses "UNION" key word and uses database specific functions, I can not use JPQL (or HQL). I did some search on Stackoverflow and threads suggest the good way would be to find out the dialect used in the application. Can anyone provide some code example?
EDIT : My apologies, I did not explain my question well enough. In my dao class implementation , I want to determine the database ( say mysql or oracle) on which my application is running and then execute the appropriate query. I need the code like jdbcTemplate.findOutTheDialect().
JPA have the native queries for that.
An example you can find here.
You can use spring JdbcTemplate to connect and query from your database.
For Example..
String query = "SELECT COUNTRY_NAME FROM COUNTRY WHERE MCC_COUNTRY NOT IN ('Reserved') ORDER BY COUNTRY_NAME";
jdbcTemplate.query(query, new ObjectRowMapper());
Where "ObjectRowMapper" will be a class to map return resultset to list of Objects.