java - EclipseLink 不使用嵌套的 Lazy OneToMany 关系填充 Lazy OneToOne

Question

我从 Hibernate 迁移到 EclipseLink，因为我们需要 EclipseLink 可以很好地处理复合主键，而 Hibernate 则不能(确实不能!)。现在我正在修复我们的 JUnit 测试，但我遇到了未加载大量 OneToMany 关系的问题。

我有以下类(class):

DatabaseSession.java

package platform.data;

import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.stream.Collectors;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
import javax.persistence.TypedQuery;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import javax.persistence.metamodel.Attribute;
import javax.persistence.metamodel.EntityType;
import javax.persistence.metamodel.Metamodel;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import platform.accesscontrol.UserContext;
import pm.data.IndicatorSet;

/**
 * Provides easy to use database sessions and transactions.
 * <p>
 * The session and transaction is automatically opened in the constructor.
 * <p>
 * The session must be closed using close(), which should be done with a try(...) { ...} block. If data is modified,
 * the transaction must be committed explicitly using commit(), usually as the last statement in the
 * try(...) { ...} block. Uncommitted transactions are automatically rolled back when the session is closed.
 */
public final class DatabaseSession implements AutoCloseable {

    /**
     * Maximum latency in milliseconds for a JPA operation, after which a warning shall be logged.
     */
    private static final double MAX_LATENCY = 100.0;

    /**
     * Maximum duration in milliseconds for a session, after which a warning shall be logged.
     */
    private static final double MAX_LATENCY_TOT = 1000.0;

    /**
     * Our logger, never null.
     */
    private static final Logger log = LoggerFactory.getLogger(DatabaseSession.class);

    /**
     * The factory for creating EntityManager instances, created in initEntityManagerFactory() or in the constructor.
     */
    private static EntityManagerFactory factory;

    /**
     * The EntityManager instance to access the database, created from the factory in the constructor.
     */
    private EntityManager em;

    /**
     * The time when the instance was created, useful for measure total time of the session.
     */
    private final long ttot = System.nanoTime();

    /**
     * Indicates whether commit() as been called.
     */
    private boolean committed;

    /**
     * Initializes the EntityManagerFactory (optional, useful for testing).
     * <p>
     * If this method is not called, the EntityManagerFactory is initialized
     * automatically with persistence unit "default" when the first instance is created.
     * <p>
     * Persistence units are defined in conf/META-INF/persistence.xml.
     *
     * @param persistenceUnitName the name of the persistence unit to be used,
     *                            must match the XML attribute /persistence/persistence-unit/@name.
     */
    public static void initEntityManagerFactory(String persistenceUnitName) {
        synchronized(DatabaseSession.class) {
            factory = Persistence.createEntityManagerFactory(persistenceUnitName);
        }
    }

    public void shutdownDB(){
        em.close();
        em = null;
        DatabaseSession.factory.close();
        DatabaseSession.factory = null;
    }

    /**
     * Opens a new session and begins a new transaction.
     */
    public DatabaseSession() {
        synchronized(DatabaseSession.class) {
            if(factory == null) {
                factory = Persistence.createEntityManagerFactory("default");
            }
        }
        createEntityManager();
    }

    public void createEntityManager(){
        em = factory.createEntityManager();
        em.getTransaction().begin();
        EntityType<IndicatorSet> entity = factory.getMetamodel().entity(IndicatorSet.class);
        Set<Attribute<IndicatorSet, ?>> attrs = entity.getDeclaredAttributes();
        attrs.toString();
    }

    @Override
    public void close() {
        try {
            if (!committed) {
                if(em != null){
                    em.getTransaction().rollback();
                }
            }
        } finally {
            if (committed) {
                if(em != null){
                    em.close();
                }
            }

            double latency = (System.nanoTime() - ttot)/1000000.0;
            if(latency > MAX_LATENCY_TOT) {
                log.warn("Duration of session was " + latency + "ms.");
            } else {
                log.debug("Duration of session was " + latency + "ms.");
            }
        }
    }

    /**
     * Commits the transaction, must explicitly be done before the session is closed.
     */
    public void commit()
    {
        long t = System.nanoTime();
        em.flush();
        em.getTransaction().commit();
        committed = true;
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of commit() was %sms.", latency);
        }
    }

    public <T extends PersistentRecord> List<T> loadAll(Class<T> clazz, String mandt) {
        return loadAll(clazz, mandt, true);
    }

    public <T extends PersistentRecord> List<T> loadAll(Class<T> clazz, String mandt, boolean filterDeleted) {
        log("loadAll(%s)", clazz.getSimpleName());
        long t = System.nanoTime();
        CriteriaBuilder b = em.getCriteriaBuilder();
        CriteriaQuery<T> q = b.createQuery(clazz);
        Metamodel m = em.getMetamodel();
        EntityType<T> et = m.entity(clazz);
        Root<T> r = q.from(clazz);
        q.select(r);
        if (mandt != null) {
            q.where(b.equal(r.get(et.getAttribute("mandt").getName()), mandt));
        }
        if (filterDeleted) {
            q.where(b.equal(r.get(et.getAttribute("deleted").getName()), 0));
        }
        List<T> result = em.createQuery(q).getResultList();
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of loadAll(%s) was %sms.", clazz.getSimpleName(), latency);
        }
        return result;
    }

    public <T extends PersistentRecord> int count(Class<T> clazz, String mandt) {
        return count(clazz, mandt, true);
    }

    public <T extends PersistentRecord> int count(Class<T> clazz, String mandt, boolean filterDeleted) {
        log("count(%s)", clazz.getSimpleName());
        long t = System.nanoTime();
        CriteriaBuilder b = em.getCriteriaBuilder();
        CriteriaQuery<T> q = b.createQuery(clazz);
        Metamodel m = em.getMetamodel();
        EntityType<T> et = m.entity(clazz);
        Root<T> r = q.from(clazz);
        q.select(r);
        if (mandt != null) {
            q.where(b.equal(r.get(et.getAttribute("mandt").getName()), mandt));
        }
        if (filterDeleted) {
            q.where(b.equal(r.get(et.getAttribute("deleted").getName()), 0));
        }
        List<T> result = em.createQuery(q).getResultList();
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of count(%s) was %sms.", clazz.getSimpleName(), latency);
        }
        return result.size();
    }

    public <T extends PersistentRecord> T load(Class<T> clazz, String mandt, String id) {
        return load(clazz, mandt, id, true);
    }

    public <T extends PersistentRecord> T load(Class<T> clazz, String mandt, String id, boolean filterDeleted) {
        log("load(%s, %s)", clazz.getSimpleName(), id);
        long t = System.nanoTime();
        T result = em.find(clazz, mandt != null ? new MandtId(mandt, id) : id);
        if(result != null){
            em.refresh(result); // TODO: This always results in a database hit, but relationship syncing is not meant to be done that way. Reduction of db hits can be achieved trough custom annotation or flag.
            //JPA does not maintain relationships for you, the application is required to set both sides to stay in sync (http://stackoverflow.com/questions/16762004/eclipselink-bidirectional-onetomany-relation)"
        }
        if(filterDeleted) {
            result = filterDeleted(result);
        }
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of load(%s, %s) was %sms.", clazz.getSimpleName(), id, latency);
        }
        return result;
    }

    public <T extends PersistentRecord> List<T> loadByQuery(Class<T> clazz, String mandt, String query, Object... params) {
        log("loadByQuery(%s, '%s', %s)", clazz.getSimpleName(), query, format(params));
        long t = System.nanoTime();
        TypedQuery<T> q = em.createQuery(query, clazz);
        for(int i = 0; i < params.length; i++) {
            q.setParameter(i+1, params[i]);
        }
        List<T> result = q.getResultList();
        if (mandt != null) { // mandt can be null to allow queries without mandt
            result = filterMandt(result, mandt); // as a safety measure we ensure mandt separation in db and application layer
        }
        result = filterDeleted(result);
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of loadByQuery(%s, '%s', %s) was %sms.", clazz.getSimpleName(), query, format(params), latency);
        }
        return result;
    }

    public <T extends PersistentRecord> T loadSingleByQuery(Class<T> clazz, String mandt, String query, Object... params) {
        log("loadSingleByQuery(%s, '%s', %s)", clazz.getSimpleName(), query, format(params));
        long t = System.nanoTime();
        TypedQuery<T> q = em.createQuery(query, clazz);
        for(int i = 0; i < params.length; i++) {
            q.setParameter(i+1, params[i]);
        }
        List<T> result = q.getResultList();
        if (mandt != null) { // mandt can be null to allow queries without mandt
            result = filterMandt(result, mandt); // as a safety measure we ensure mandt separation in db and application layer
        }
        result = filterDeleted(result);
        double latency = (System.nanoTime() - t)/1000000.0;
        if(latency > MAX_LATENCY) {
            warn("Latency of loadSingleByQuery(%s, '%s', %s) was %sms.", clazz.getSimpleName(), query, format(params), latency);
        }
        return result.size() > 0 ? result.get(0) : null;
    }

    /**
     * Stores a new or updated record (resulting in an INSERT or UPDATE statement)
     * @param record the record to be stored, must not be null.
     * @param uc the user that initiated the operation, can be null.
     * @return the given record, or another instance with the same ID if EntityManager.merge() was called.
     */
    public <T extends PersistentRecord> T store(T record, UserContext uc) {
        if(record == null) {
            return null;
        }
        log("update(%s, %s)", record.getClass().getSimpleName(), record.getId());
        if(record instanceof ReadWriteRecord) {
            ((ReadWriteRecord)record).touch(uc);
        }
        return add(record);
    }

    /**
     * Deletes a record or marks a record as deleted (resulting in an UPDATE or maybe an INSERT statement if T is a subclass of ReadWriteRecord, or resulting in a DELETE statement otherwise).
     * @param record the record to be deleted, must not be null.
     * @param uc the user that initiated the operation, can be null.
     * @return the given record, or another instance with the same ID if EntityManager.merge() was called.
     */
    public <T extends PersistentRecord> T delete(T record, UserContext uc) {
        if(record == null) {
            return null;
        }
        log("delete(%s, %s)", record.getClass().getSimpleName(), record.getId());
        if(record instanceof ReadWriteRecord) {
            ((ReadWriteRecord)record).setDeleted(true);
            ((ReadWriteRecord)record).touch(uc);
            return add(record); // same as store(), we _dont_ physically delete the record
        } else {
            em.remove(record);
            return null;
        }
    }

    /**
     * Physically deletes all records of a table, intended for JUnit tests only (unless you really want to get rid of your data).
     * @param clazz the DTO class of the table.
     */
    public <T extends PersistentRecord> void deleteAll(Class<T> clazz, String mandt) {
        log("deleteAll(%s)", clazz.getSimpleName());
        for(T rec : loadAll(clazz, mandt, false)) {
            em.remove(rec);
        }
    }

    /**
     * Forces lazy initialization of an entity.
     * @param record a record loaded from the database, can be null.
     * @return the record passed to this method.
     */
    public <T extends PersistentRecord> T fetch(T record) {
        if(record != null) {
            em.refresh(record);// TODO: This always results in a database hit, but relationship syncing is not meant to be done that way. Reduction of db hits can be achieved trough custom annotation or flag.
            //JPA does not maintain relationships for you, the application is required to set both sides to stay in sync (http://stackoverflow.com/questions/16762004/eclipselink-bidirectional-onetomany-relation)
            record.fetch();
        }
        return record;
    }

    /**
     * Forces lazy initialization of an entity.
     * @param record a record loaded from the database, can be null.
     * @param fetcher a method to be invoked on the record to lazy initialize nested fields.
     * @return the record passed to this method.
     */
    public <T extends PersistentRecord> T fetch(T record, BiConsumer<DatabaseSession, T> fetcher) {
        if(record != null) {
            em.refresh(record); // TODO: This always results in a database hit, but relationship syncing is not meant to be done that way. Reduction of db hits can be achieved trough custom annotation or flag.
            //JPA does not maintain relationships for you, the application is required to set both sides to stay in sync (http://stackoverflow.com/questions/16762004/eclipselink-bidirectional-onetomany-relation)
            record.fetch();
            fetcher.accept(this, record);
        }
        return record;
    }

    /**
     * Forces lazy initialization of multiple entities.
     * @param records a list of records loaded from the database, can be null.
     * @param fetcher a method to be invoked on the records to lazy initialize nested fields.
     * @return the list of records passed to this method.
     */
    public <T extends PersistentRecord> List<T> fetch(List<T> records, BiConsumer<DatabaseSession, T> fetcher) {
        if(records != null) {
            for(T record : records) {
                em.refresh(record); // TODO: This always results in a database hit, but relationship syncing is not meant to be done that way. Reduction of db hits can be achieved trough custom annotation or flag.
                //JPA does not maintain relationships for you, the application is required to set both sides to stay in sync (http://stackoverflow.com/questions/16762004/eclipselink-bidirectional-onetomany-relation)
                record.fetch();
                fetcher.accept(this, record);
            }
        }
        return records;
    }

    /**
     * Forces lazy initialization of a one-to-many relationship.
     * @param records a list representing a one-to-many relationship, can be null.
     * @return the relationship passed to this method.
     */
    public <T extends PersistentRecord> List<T> fetchCollection(List<T> records) {
        if(records != null) {
            records.size();
        }
        return records;
    }

    /**
     * Adds the given record to the EntityManager, called by store() and delete().
     * <p>
     * This method attempts to do something like Hibernate's saveOrUpdate(), which is not available in JPA:
     * <ul>
     * <li> For newly created records, EntityManager.persist() has to be called in order so insert the record.
     *      This case will be assumed when markNew() has been called on the record.
     * <li> For records that have been read from the database by _another_ session (so-called detached entities),
     *      EntityManager.merge() has to be called in order to update the record.
     *      This case will be assumed when markNew() has NOT been called on the record.
     * <li> For records that have been read from the database by this session, nothing has to be done because the
     *      EntityManager takes care of the entities it loaded. This case can be detected easily using contains().
     * </ul>
     * Note: EntityManager.merge() does not add the entity to the session.
     * Instead, a new entity is created and all properties are copied from the given record to the new entity.
     *
     * @param record the record to be added, can be null.
     * @return the given record, or another instance with the same ID if EntityManager.merge() was called.
     */
    private <T extends PersistentRecord> T add(T record) {
        long t = System.nanoTime();
        try {
            if (record == null || em.contains(record)) {
                return record;
            } else if(record.mustInsert) {
                em.persist(record); // will result in INSERT
                record.mustInsert = false;
                return record;
            } else {
                record = em.merge(record);
                return record;
            }
        } finally {
            double latency = (System.nanoTime() - t)/1000000.0;
            if(latency > MAX_LATENCY) {
                warn("Latency of add(%s, %s) was %sms.", record.getClass().getSimpleName(), record.getId(), latency);
            }
        }
    }

    private static <T extends PersistentRecord> List<T> filterDeleted(List<T> records) {
        if(records != null) {
            records = records.stream().
                    filter(record -> (record instanceof ReadWriteRecord) == false || ((ReadWriteRecord) record).getDeleted() == false).
                    collect(Collectors.toList());
        }
        return records;
    }

    private static <T extends PersistentRecord> List<T> filterMandt(List<T> records, String mandt) {
        if(records != null) {
            records = records.stream().
                    filter(record -> Objects.equals(record.getMandt(), mandt)).
                    collect(Collectors.toList());
        }
        return records;
    }

    private static <T extends PersistentRecord> T filterDeleted(T record) {
        if(record != null && record instanceof ReadWriteRecord) {
            if(((ReadWriteRecord) record).getDeleted()) {
                record = null;
            }
        }
        return record;
    }

    private void log(String format, Object... args) {
        if(log.isDebugEnabled()) {
            log.debug(String.format(format, args));
        }
    }

    private void warn(String format, Object... args) {
        if(log.isWarnEnabled()) {
            log.warn(String.format(format, args));
        }
    }

    private static String format(Object... args) {
        StringBuilder sb = new StringBuilder();
        sb.append("[");
        for(Object arg: args) {
            if(sb.length() > 1)
                sb.append(", ");
            sb.append(arg);
        }
        sb.append("]");
        return sb.toString();
    }

    // For debugging
    public Query createQuery(String string) {
        return em.createQuery(string);
    }

}

Project.java

package pm.data;

...common imports...

import platform.data.DatabaseBindingIds;
import platform.data.MandtId;
import platform.data.PropertySet;
import platform.data.ReadWriteRecord;
import resource.data.Resource;

@Entity
@IdClass(MandtId.class)
public class Project extends ReadWriteRecord {

    @Id
    @Column(name=DatabaseBindingIds.PROJECT_TENANT)
    private String mandt;

    @Id
    @Column(name=DatabaseBindingIds.PROJECT_ID)
    private String entityId;

    @OneToOne(fetch=FetchType.LAZY, cascade= CascadeType.ALL) // one to one mappings are directly mapped using the project primary keys
    @JoinColumns( {
        @JoinColumn(name=DatabaseBindingIds.PROJECT_TENANT, referencedColumnName=DatabaseBindingIds.PROPERTYSET_TENANT, insertable=false, updatable=false),
        @JoinColumn(name=DatabaseBindingIds.PROJECT_ID, referencedColumnName=DatabaseBindingIds.PROPERTYSET_ID, insertable=false, updatable=false)
    } )
    private PropertySet propertySet;

    @OneToOne(fetch=FetchType.LAZY, cascade = CascadeType.ALL) // one to one mappings are directly mapped using the project report primary keys
    @JoinColumns( {
        @JoinColumn(name=DatabaseBindingIds.PROJECTREPORT_TENANT, referencedColumnName=DatabaseBindingIds.INDICATORSET_TENANT, insertable=false, updatable=false),
        @JoinColumn(name=DatabaseBindingIds.PROJECTREPORT_ID, referencedColumnName=DatabaseBindingIds.INDICATORSET_ID, insertable=false, updatable=false)
    } )
    private IndicatorSet indicatorSet; // SAMPLE NOTE: The indicator set is essentially the same thing as the property set. 


    ...other member variables...

    @Override
    public String getMandt() {
        return mandt;
    }

    @Override
    public String getId() {
        return entityId;
    }

    @Override
    public void setId(MandtId x) {
        markNew();
        mandt = x != null ? x.getMandt() : null;
        entityId = x != null ? x.getId() : null;
        propertySet = new PropertySet();
        propertySet.setId(x);
    }

    public PropertySet getPropertySet() {
        return propertySet;
    }


    ...getters and setters for other member variables...
}

PropertySet.java

package platform.data;

import java.util.ArrayList;
import java.util.List;

...common imports...

@Entity
@IdClass(MandtId.class)
public class PropertySet extends ReadWriteRecord {

    @Id
    @Column(name=DatabaseBindingIds.PROPERTYSET_TENANT)
    private String mandt;

    @Id
    @Column(name=DatabaseBindingIds.PROPERTYSET_ID)
    private String entityId;

    @OneToMany(mappedBy="propertySet", fetch=FetchType.EAGER)
    @OrderBy("sortIndex")
    private List<Property> properties;

    @Override
    public String getMandt() {
        return mandt;
    }

    @Override
    public String getId() {
        return entityId;
    }

    @Override
    public void setId(MandtId x) {
        markNew();
        mandt = x != null ? x.getMandt() : null;
        entityId = x != null ? x.getId() : null;
    }

    public List<Property> getProperties() {
        if(properties == null) {
            properties = new ArrayList<>();
        }
        return properties;
    }
}

Property.java

package platform.data;

...common imports...

@Entity
@IdClass(MandtId.class)
public class Property extends ReadWriteRecord {

    @Id
    @Column(name=DatabaseBindingIds.PROPERTY_TENANT)
    private String mandt;

    @Id
    @Column(name=DatabaseBindingIds.PROPERTY_ID)
    private String entityId;

    @ManyToOne(fetch=FetchType.EAGER, optional=false)
    @JoinColumns( {
        @JoinColumn(name=DatabaseBindingIds.PROPERTY_TENANT, referencedColumnName=DatabaseBindingIds.PROPERTYSET_TENANT, insertable=false, updatable=false),
        @JoinColumn(name=DatabaseBindingIds.PROPERTY_PROPERTYSET_ID, referencedColumnName=DatabaseBindingIds.PROPERTYSET_ID, insertable=true, updatable=true)
    } )
    private PropertySet propertySet;

    @Column
    private Integer sortIndex;

    @Column
    private String key;

    @Column
    @Convert(converter = IntlStringConverter.class)
    private IntlString label;

    @Column
    private String type;

    @Column
    private String value;

    @Override
    public String getMandt() {
        return mandt;
    }

    @Override
    public String getId() {
        return entityId;
    }

    @Override
    public void setId(MandtId x) {
        markNew();
        mandt = x != null ? x.getMandt() : null;
        entityId = x != null ? x.getId() : null;
    }

    public void setPropertySet(PropertySet x) {
        propertySet = x;
    }

    public PropertySet getPropertySet() {
        return propertySet;
    }

    public int getSortIndex() {
        return sortIndex == null ? 0 : sortIndex;
    }

    public void setSortIndex(int x) {
        sortIndex = x;
    }

    public String getKey() {
        return key;
    }

    public void setKey(String x) {
        key = x;
    }

    public IntlString getLabel() {
        return label;
    }

    public void setLabel(IntlString x) {
        label = x;
    }

    public String getType() {
        return type;
    }

    public void setType(String x) {
        type = x;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String x) {
        value = x;
    }
}

MandtId.java复合主键IDClass。

package platform.data;

import java.io.Serializable;
import java.util.Objects;

/**
 * @author sm
 * Class to map MANDT and *ID field as composite key
 */
@SuppressWarnings("serial")
public class MandtId implements Serializable {

    private String mandt;
    private String entityId;

    ...setters and getters...

    @Override
    public int hashCode()
    ...

    @Override
    public boolean equals(Object other)
    ...

    @Override
    public String toString()
    ...

}

我们在每个单元测试之前插入条目，如下所示:

try(DatabaseSession db = new DatabaseSession()) {


    Project prjT = createProject(db, UUID_PROJECT_NEW, "<New Project>");
    createProperty(db, prjT.getPropertySet(), "prj-prop1", "Property 1", "string", "<New Value 1>", 2);
    createProperty(db, prjT.getPropertySet(), "prj-prop2", "Property 2", "string", "<New Value 2>", 1);

    db.commit();
}

public static Project createProject(DatabaseSession db, String id, String name) {
    Project prj = new Project();
    prj.setId(new MandtId(MANDT, id));
    prj.setName(name);
    prj.setStatus(UUID_PROJECT_STATUS_ACTIVE);
    db.store(prj.getPropertySet(), null); // workaround: persist child first (otherwise PropertySet will stay marked as new)
    db.store(prj, null);
    return prj;
}

    public static Property createProperty(DatabaseSession db, PropertySet ps, String key, String label, String type, String value, int sortIndex) {
    Property rec = new Property();
    rec.setId(new MandtId(MANDT, UuidString.generateNew()));
    rec.setPropertySet(ps);
    rec.setKey(key);
    rec.setLabel(IntlStrings.wrap(label));
    rec.setType(type);
    rec.setValue(value);
    rec.setSortIndex(sortIndex);
    ps.getProperties().add(rec);
    db.store(rec.getPropertySet(), null);
    db.store(rec, null);
    // rec.properties.add(p);
    return rec;
}

如果我稍后尝试获得该项目，我会:

@Override
public Project loadProject(String projectId) throws DataAccessException {
    try(DatabaseSession session = new DatabaseSession()) {
        return session.fetch(session.load(Project.class, mandt, projectId), (s, r) -> {
            s.fetch(r.getPropertySet());
            s.fetch(r.getOwner());
            s.fetch(r.getResponsibility());
            s.fetch(r.getProjectGuideline());
        });
    } catch(RuntimeException e) {
        throw new DataAccessException(e);
    }
}

但在这种情况下，属性集保持为空。它甚至没有初始化。当我初始化它时，它保持为空。我可以通过使用 em.refresh 来修复其他获取，但我已经添加了一个 TODO，因为刷新总是会导致数据库命中。属性实体位于数据库中，我可以通过单独的特定 SELECT 查询找到它。

这个数据库设置的主要要求是我们支持数据库内容的高并发编辑。由于数据库通过原子化提交来修复并发问题，因此我认为我在这里不会出现竞争。

我看到的一个问题是，在添加具有双向关系的实体时，我不会将它们添加到两侧，但是当我稍后再次加载它们时，这个问题不应该再次修复吗(可能不是因为它们被缓存了)？此外，它并没有解决我在直接 OneToMany 关系中遇到的任何其他问题(与此处具有嵌套 OneToMany 的 OneToOne 相比)，我仍然需要 em.refresh(...)。如果在服务器环境中，em 是否以无竞争的方式维护实体？

如果您需要更多信息，请告诉我。

编辑:

这个问题似乎与我在这里所做的单元测试的设置有关，内存中的 H2 数据库似乎与 eclipselink 混淆，但是以下注释在生产系统中工作得很好(MsSQL 上的 eclipselink):

Project.java

package pm.data;

...common imports...

import platform.data.DatabaseBindingIds;
import platform.data.MandtId;
import platform.data.PropertySet;
import platform.data.ReadWriteRecord;
import resource.data.Resource;

@Entity
@IdClass(MandtId.class)
public class Project extends ReadWriteRecord {

    @Id
    @Column(name=DatabaseBindingIds.PROJECT_TENANT)
    private String mandt;

    @Id
    @Column(name=DatabaseBindingIds.PROJECT_ID)
    private String entityId;

    @OneToOne(fetch=FetchType.LAZY, cascade= CascadeType.ALL) // one to one mappings are directly mapped using the project primary keys
    @JoinColumns( {
        @JoinColumn(name=DatabaseBindingIds.PROJECT_TENANT, referencedColumnName=DatabaseBindingIds.PROPERTYSET_TENANT, insertable=false, updatable=true),
        @JoinColumn(name=DatabaseBindingIds.PROJECT_ID, referencedColumnName=DatabaseBindingIds.PROPERTYSET_ID, insertable=false, updatable=true)
    } )
    private PropertySet propertySet;

    @OneToOne(fetch=FetchType.LAZY, cascade = CascadeType.ALL) // one to one mappings are directly mapped using the project report primary keys
    @JoinColumns( {
        @JoinColumn(name=DatabaseBindingIds.PROJECTREPORT_TENANT, referencedColumnName=DatabaseBindingIds.INDICATORSET_TENANT, insertable=false, updatable=false),
        @JoinColumn(name=DatabaseBindingIds.PROJECTREPORT_ID, referencedColumnName=DatabaseBindingIds.INDICATORSET_ID, insertable=false, updatable=false)
    } )
    private IndicatorSet indicatorSet; // NOTE: Yes, the updatable are false here and are only true in one set.


    ...other member variables...

    ...same as above...


    ...getters and setters for other member variables...
}

PropertySet.java

package platform.data;

import java.util.ArrayList;
import java.util.List;

...common imports...

@Entity
@IdClass(MandtId.class)
@Cache(isolation=CacheIsolationType.ISOLATED) // Fix turns off EclipseLink cache for PropertySet
public class PropertySet extends ReadWriteRecord {

    ...same as above...

我接受了克里斯的回答，因为它帮助我理解了发生的问题以及缓存的工作原理。对于 PropertySet，我必须关闭缓存。解决问题的选项列表也非常有帮助。

Answer 1

您提到的问题与 Project->PropertySet 关系有关，这是严格的 OneToOne 映射，并且显示的实体没有显示问题涉及 OneToMany。由于不是双向的，所以和传统的不设置后退指针没有关系，但还是有一定关系的

问题是因为此 OneToOne 映射的外键也是项目 ID 字段，这些字段被映射为可写的基本映射。为了解决多个可写映射异常，您将 Project.propertySet 映射的连接列标记为 insertable=false、updatable=false，本质上是告诉 EclipseLink 该映射是只读的。因此，当您设置或更改关系时，此“更改”将被忽略并且不会合并到缓存中。这会导致您创建的实体在从缓存中读取时该引用始终为空，除非从数据库中刷新/重新加载该实体。这仅影响二级缓存，因此不会显示在创建它的 EntityManager 中，除非清除它。

有几种方法可以解决这个问题，哪种方法最好取决于您的应用程序的使用情况。

1. 禁用共享缓存。这可以针对每个实体或针对特定实体来完成。看eclipseLink faq了解详情。这是最简单的选择会给你类似于 Hibernate 的结果，它不启用默认情况下二级缓存，但不推荐这样做，除非有不使用二级缓存的其他考虑因素，因为它以性能为代价。

2. 更改要使用的 Project 中的基本 ID 映射字段可插入=假，可更新=假。然后您删除从连接列可插入=假，可更新=假，允许OneToOne 映射来控制您的主键。功能上这个不应以任何方式更改您的应用程序。如果你得到同样的基本映射问题， native EclipseLink postClone方法可用于设置引用映射中的字段，或者您的实体 get 方法可以快速检查是否存在 PropertySet并在返回 null 之前使用该值。

3. 使用 JPA 2.0 的派生 ID。 JPA 允许将关系标记为 ID，从而无需为同一值提供这两个基本映射。或者，您可以在关系上使用 @MapsId 来告诉 JPA 该关系控制该值，JPA 将为您设置这些字段。使用 @MapsId 需要使用您的 pk 类作为嵌入式 ID，并且看起来像:

   @Entity
   public class Project extends ReadWriteRecord {
   
       @EmbeddedId
       private MandtId mandtId;
   
       @MapsId("mandtId")
       @OneToOne(fetch=FetchType.LAZY, cascade= CascadeType.ALL) // one to one mappings are directly mapped using the project primary keys
       @JoinColumns( {
           @JoinColumn(name=DatabaseBindingIds.PROJECT_TENANT, referencedColumnName=DatabaseBindingIds.PROPERTYSET_TENANT, insertable=false, updatable=false),
           @JoinColumn(name=DatabaseBindingIds.PROJECT_ID, referencedColumnName=DatabaseBindingIds.PROPERTYSET_ID, insertable=false, updatable=false)
       } )
       private PropertySet propertySet;