I want to convert List< Long> to Maybe>. Here is example.
class Structure
{
Long id;
Long data;
}
class makeStructure{
Maybe<Structure> getStructure(Long id)
{
return someMaybe;
}
}
if the origin data is like below.
1. Structure{ id : 100, data :200}
2. Structure{ id : 101, data :201}
I want to convert it to Maybe< Map< Long, Structure>> containing below two data.
(Structure id used as key)
1. (100, Structure{ id : 100, data :200})
2. (101, Structure{ id : 101, data :201})
I tried something like below.
List<Long> list;//somethig in it
makeStructure makeStructrue = new makeStructure();
Map<Long, Structure> result = list.stream()
.map(i->makeStructrue.getStructure(i))
.map(v->v.blockingGet())
.collect(Collector.toMap(k->k.getId(),k->k);
return Maybe.just(result);
But this is not the result that i want in two reason.
First, I used blockGet method
Second, the result of collect is Map not Maybe. I wonder just using Maybe.just(result) ensure the same result.
to get a good performance I tried not to use blockingGet();
Is there any good idea to make clean code?
Related
I'm struggling to trying the pagination feature, as described in the reference document.
This is my table schema:
CREATE TABLE cities
(
id int PRIMARY KEY,
name varchar(255),
pref_id int
);
Repository:
public interface CityRepository extends CrudRepository<CityEntity, Integer> {
Page<CityEntity> findAll(Pageable pageable);
// get all cities in the prefecture
Page<CityEntity> findByPrefId(Integer prefId, Pageable pageable);
}
Test code:
Page<CityEntity> allCities = repository.findAll(PageRequest.of(0, 10));
Page<CityEntity> cities = repository.findByPrefId(1, PageRequest.of(0, 10));
findAll works well, but findByPrefId throws the following error:
Incorrect result size: expected 1, actual 10
org.springframework.dao.IncorrectResultSizeDataAccessException: Incorrect result size: expected 1, actual 10
at org.springframework.dao.support.DataAccessUtils.nullableSingleResult(DataAccessUtils.java:100)
at org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate.queryForObject(NamedParameterJdbcTemplate.java:237)
at org.springframework.data.jdbc.repository.query.AbstractJdbcQuery.lambda$singleObjectQuery$1(AbstractJdbcQuery.java:115)
at org.springframework.data.jdbc.repository.query.PartTreeJdbcQuery.execute(PartTreeJdbcQuery.java:98)
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor$QueryMethodInvoker.invoke(QueryExecutorMethodInterceptor.java:195)
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:152)
at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:130)
...
If I change the method signature into List<CityEntity> findByPrefId(Integer prefId, Pageable pageable), it works.
Am I missing something? I'm using the latest version of spring-data-jdbc (2.0.2.RELEASE).
I don't know about the technicality, but this is what I learned from experience.
In your case, if the total number of cities is lesser than the pageable.getPageSize(), then your repository will return a List<>.
But if total number of cities is bigger than the pageable.getPageSize() then your repository will return a Page<>.
Knowing that, this is what I did to work around it.
Long amount = repository.countByPrefId(prefId);
if(pagination.getPageSize()>amount ) {
List<CityEntity> list = repository.findByPrefId(prefId);
} else {
Page<CityEntity> pages = repository.findByPrefId(person, PageRequest.of(0, 10));
}
This also means that in your repository you'll have two differents methods, one with Pageable as a parameter and one with only PrefId as a parameter.
I believe the accepted answer is referring to Spring Data JPA which does work by returning pages based on a count query derived from the custom query OR manually set via countQuery, no reason for the if/else.
However this flat out does not work in Spring Data JDBC.
https://jira.spring.io/browse/DATAJDBC-554
Workaround provided in link but for reference:
interface FooRepository extends PagingAndSortingRepository<FooEntity, Long> {
List<FooEntity> findAllByBar(String bar, Pageable pageable);
Long countAllByBar(String bar);
}
And then combining those 2 queries like this:
List<FooEntity> fooList = repository.findAllByBar("...", pageable);
Long fooTotalCount = repository.countAllByBar("...");
Page<FooEntity> fooPage = PageableExecutionUtils.getPage(fooList, pageable, () -> fooTotalCount);
I have a document like that:
'subject' : {
'name' :"...."
'facebookPosts':[
{
date:"14/02/2017 20:20:03" , // it is a string
text:"facebook post text here",
other stuff here
}
]
}
and I want to count the facebookPosts within a specific objects that their date field contains e.g "23/07/2016".
Now, I do that by extracting all the documents and count in the client side (spring ) , But I think that's not efficient.
You need to aggregate your results.
final Aggregation aggregation = Aggregation.newAggregation(
Aggregation.match(Criteria.where("facebookPosts.date").regex(REGEX)),
Aggregation.unwind("facebookPosts"),
Aggregation.group().count().as("count"));
Regex might not be the best solution, just an example.
unwind will split array into separate elements you can then count.
Create a class that will hold the count, something like:
public class PostCount {
private Long count;
// getters, setters
}
And then execute it like this:
AggregationResults<PostCount> postCount = mongoTemplate.aggregate(aggregation, Subject.class, PostCount.class);
long count = postCount.getMappedResults().get(0).getCount();
I've got some working, inelegant code here:
The custom object is:
public class Person {
private int id;
public getId() { return this.id }
}
And I have a Class containing a Set<Person> allPersons containing all available subjects. I want to extract a new Set<Person> based upon one or more ID's of my choosing. I've written something which works using a nested enhanced for loop, but it strikes me as inefficient and will make a lot of unnecessary comparisons. I am getting used to working with Java 8, but can't quite figure out how to compare the Set against an Array. Here is my working, but verbose code:
public class MyProgram {
private Set<Person> allPersons; // contains 100 people with Ids 1-100
public Set<Person> getPersonById(int[] ids) {
Set<Person> personSet = new HashSet<>() //or any type of set
for (int i : ids) {
for (Person p : allPersons) {
if (p.getId() == i) {
personSet.add(p);
}
}
}
return personSet;
}
}
And to get my result, I'd call something along the lines of:
Set<Person> resultSet = getPersonById(int[] intArray = {2, 56, 66});
//resultSet would then contain 3 people with the corresponding ID
My question is how would i convert the getPersonById method to something using which streams allPersons and finds the ID match of any one of the ints in its parameter array? I thought of some filter operation, but since the parameter is an array, I can't get it to take just the one I want only.
The working answer to this is:
return allPersons.stream()
.filter(p -> (Arrays.stream(ids).anyMatch(i -> i == p.getId())) )
.collect(Collectors.toSet());
However, using the bottom half of #Flown's suggestion and if the program was designed to have a Map - it would also work (and work much more efficiently)
As you said, you can introduce a Stream::filter step using a Stream::anyMatch operation.
public Set<Person> getPersonById(int[] ids) {
Objects.requireNonNull(ids);
if (ids.length == 0) {
return Collections.emptySet();
}
return allPersons.stream()
.filter(p -> IntStream.of(ids).anyMatch(i -> i == p.getId()))
.collect(Collectors.toSet());
}
If the method is called more often, then it would be a good idea to map each Person to its id having a Map<Integer, Person>. The advantage is, that the lookup is much faster than iterating over the whole set of Person.Then your algorithm may look like this:
private Map<Integer, Person> idMapping;
public Set<Person> getPersonById(int[] ids) {
Objects.requireNonNull(ids);
return IntStream.of(ids)
.filter(idMapping::containsKey)
.mapToObj(idMapping::get)
.collect(Collectors.toSet());
}
Is it possible to fetch data in user defined ranges [int starting record -int last record]?
In my case user will define in query String in which range he wants to fetch data.
I have tried something like this
Pageable pageable = new PageRequest(0, 10);
Page<Project> list = projectRepository.findAll(spec, pageable);
Where spec is my defined specification but unfortunately this do not help.
May be I am doing something wrong here.
I have seen other spring jpa provided methods but nothing are of much help.
user can enter something like this localhost:8080/Section/employee? range{"columnName":name,"from":6,"to":20}
So this says to fetch employee data and it will fetch the first 15 records (sorted by columnName ) does not matter as of now.
If you can suggest me something better that would be great.if you think I have not provided enough information please let me know, I will provide required information.
Update :I do not want to use native or Create query statements (until I don't have any other option).
May be something like this:
Pageable pageable = new PageRequest(0, 10);
Page<Project> list = projectRepository.findAll(spec, new pageable(int startIndex,int endIndex){
// here my logic.
});
If you have better options, you can suggest me that as well.
Thanks.
Your approach didn't work, because new PageRequest(0, 10); doens't do what you think. As stated in docs, the input arguments are page and size, not limit and offset.
As far as I know (and somebody correct me if I'm wrong), there is no "out of the box" support for what you need in default SrpingData repositories. But you can create custom implementation of Pagable, that will take limit/offset parameters. Here is basic example - Spring data Pageable and LIMIT/OFFSET
We can do this with Pagination and by setting the database table column name, value & row counts as below:
#Transactional(readOnly=true)
public List<String> queryEmployeeDetails(String columnName,String columnData, int startRecord, int endRecord) {
Query query = sessionFactory.getCurrentSession().createQuery(" from Employee emp where emp.col= :"+columnName);
query.setParameter(columnName, columnData);
query.setFirstResult(startRecord);
query.setMaxResults(endRecord);
List<String> list = (List<String>)query.list();
return list;
}
If I am understanding your problem correctly, you want your repository to allow user to
Provide criteria for query (through Specification)
Provide column to sort
Provide the range of result to retrieve.
If my understanding is correctly, then:
In order to achieve 1., you can make use of JpaSpecificationExecutor from Spring Data JPA, which allow you to pass in Specificiation for query.
Both 2 and 3 is achievable in JpaSpecificationExecutor by use of Pagable. Pageable allow you to provide the starting index, number of record, and sorting columns for your query. You will need to implement your range-based Pageable. PageRequest is a good reference on what you can implement (or you can extend it I believe).
So i got this working as one of the answer suggested ,i implemented my own Pageable and overrided getPagesize(),getOffset(),getSort() thats it.(In my case i did not need more)
public Range(int startIndex, int endIndex, String sortBy) {
this.startIndex = startIndex;
this.endIndex = endIndex;
this.sortBy = sortBy;
}
#Override
public int getPageSize() {
if (endIndex == 0)
return 0;
return endIndex - startIndex;
}
#Override
public int getOffset() {
// TODO Auto-generated method stub
return startIndex;
}
#Override
public Sort getSort() {
// TODO Auto-generated method stub
if (sortBy != null && !sortBy.equalsIgnoreCase(""))
return new Sort(Direction.ASC, sortBy);
else
return new Sort(Direction.ASC, "id");
}
where startIndex ,endIndex are starting and last index of record.
to access it :
repository.findAll(spec,new Range(0,20,"id");
There is no offset parameter you can simply pass. However there is a very simple solution for this:
int pageNumber = Math.floor(offset / limit) + ( offset % limit );
PageRequest pReq = PageRequest.of(pageNumber, limit);
The client just have to keep track on the offset instead of page number. By this I mean your controller would receive the offset instead of the page number.
Hope this helps!
getSimpleJdbcTemplate().query(sql, getMapper()); returns List, but I need a Map where key will be store data of one of the field of object. For example, I have object named "Currency" which has fields: id, code, name, etc. Code above will return List object, but I want to get currency by id from Map. Now, I wrote the following code:
#Override
public Map<Integer, Currency> listCurrencies() {
String sql = "select cur_id, cur_code, cur_name ... from currencies";
List<Currency> currencies = getSimpleJdbcTemplate().query(sql, getMapper());
Map<Integer, Currency> map = new HashMap<Integer, Currency>(currencies.size());
for (Currency currency : currencies) {
map.put(currency.getId(), currency);
}
return map;
}
Are there any way to do same but without creating List object and looping inside it?
You have ResultSetExtractor for extracting values from the ResultSet. So in your case you can write a custom ResultSetExtractor which will return you the Map object.