How to use

findById

method

in

org.springframework.data.jpa.repository.support.SimpleJpaRepository

/**
 * 基于主键查询单一数据对象
 * @param id
 * @return
@Transactional(readOnly = true)
public Optional<T> findOptionalOne(ID id) {
  return jpaRepository.findById




    
(id);

/**
 * 基于主键查询单一数据对象
 * @param id
 * @return
@Transactional(readOnly = true)
public T findOne(ID id) {
  return jpaRepository.findById(id).orElse(null);

@Transactional
public void deleteById(ID id) {
  Assert.notNull(id, ID_MUST_NOT_BE_NULL);
  delete(findById(id).orElseThrow(() -> new EmptyResultDataAccessException(
      String.format("No %s entity with id %s exists!", entityInformation.getJavaType(), id), 1)));

public List<T> findAllById(Iterable<ID> ids) {
  Assert.notNull(ids, "The given Iterable of Id's must not be null!");
  if (!ids.iterator().hasNext()) {
    return Collections.emptyList();
  if (entityInformation.hasCompositeId()) {
    List<T> results = new ArrayList<T>();
    for (ID id : ids) {
      




    
findById(id).ifPresent(results::add);
    return results;
  ByIdsSpecification<T> specification = new ByIdsSpecification<T>(entityInformation);
  TypedQuery<T> query = getQuery(specification, Sort.unsorted());
  return query.setParameter(specification.parameter, ids).getResultList();

public




    
 boolean existsById(ID id) {
  Assert.notNull(id, ID_MUST_NOT_BE_NULL);
  if (entityInformation.getIdAttribute() == null) {
    return findById(id).isPresent();
  String placeholder = provider.getCountQueryPlaceholder();
  String entityName = entityInformation.getEntityName();
  Iterable<String> idAttributeNames = entityInformation.getIdAttributeNames();
  String existsQuery = QueryUtils.getExistsQueryString(entityName, placeholder, idAttributeNames);
  TypedQuery<Long> query = em.createQuery(existsQuery, Long.class);
  if (!entityInformation.hasCompositeId()) {
    query.setParameter(idAttributeNames.iterator().next(), id);
    return query.getSingleResult() == 1L;
  for (String idAttributeName : idAttributeNames) {
    Object idAttributeValue = entityInformation.getCompositeIdAttributeValue(id, idAttributeName);
    boolean complexIdParameterValueDiscovered = idAttributeValue != null
        && !query.getParameter(idAttributeName).getParameterType().isAssignableFrom(idAttributeValue.getClass());
    if (complexIdParameterValueDiscovered) {
      // fall-back to findById(id) which does the proper mapping for the parameter.
      return findById(id).isPresent();
    query.setParameter(idAttributeName, idAttributeValue);
  return query.getSingleResult() == 1L;