聊聊dddsample-core的model

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本文主要研究一下dddsample-core的model

Entity

public interface Entity<T> {

  /**
   * Entities compare by identity, not by attributes.
   *
   * @param other The other entity.
   * @return true if the identities are the same, regardless of other attributes.
   */
  boolean sameIdentityAs(T other);

}
Entity接口定义了sameIdentityAs方法

ValueObject

public interface ValueObject<T> extends Serializable {

  /**
   * Value objects compare by the values of their attributes, they don't have an identity.
   *
   * @param other The other value object.
   * @return <code>true</code> if the given value object's and this value object's attributes are the same.
   */
  boolean sameValueAs(T other);

}
ValueObject接口定义了sameValueAs方法

TrackingId

public final class TrackingId implements ValueObject<TrackingId> {

  private String id;

  /**
   * Constructor.
   *
   * @param id Id string.
   */
  public TrackingId(final String id) {
    Validate.notNull(id);
    this.id = id;
  }

  /**
   * @return String representation of this tracking id.
   */
  public String idString() {
    return id;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    TrackingId other = (TrackingId) o;

    return sameValueAs(other);
  }

  @Override
  public int hashCode() {
    return id.hashCode();
  }

  @Override
  public boolean sameValueAs(TrackingId other) {
    return other != null && this.id.equals(other.id);
  }

  @Override
  public String toString() {
    return id;
  }

  TrackingId() {
    // Needed by Hibernate
  }
}
TrackingId实现了ValueObject接口,sameValueAs方法通过equals方法判断

Type

  public enum Type implements ValueObject<Type> {
    LOAD(true),
    UNLOAD(true),
    RECEIVE(false),
    CLAIM(false),
    CUSTOMS(false);

    private final boolean voyageRequired;

    /**
     * Private enum constructor.
     *
     * @param voyageRequired whether or not a voyage is associated with this event type
     */
    private Type(final boolean voyageRequired) {
      this.voyageRequired = voyageRequired;
    }

    /**
     * @return True if a voyage association is required for this event type.
     */
    public boolean requiresVoyage() {
      return voyageRequired;
    }

    /**
     * @return True if a voyage association is prohibited for this event type.
     */
    public boolean prohibitsVoyage() {
      return !requiresVoyage();
    }

    @Override
    public boolean sameValueAs(Type other) {
      return other != null && this.equals(other);
    }

  }
Type枚举实现了ValueObject接口,其sameValueAs方法通过equals判断

DomainEvent

public interface DomainEvent<T> {

  /**
   * @param other The other domain event.
   * @return <code>true</code> if the given domain event and this event are regarded as being the same event.
   */
  boolean sameEventAs(T other);

}
DomainEvent接口定义了sameEventAs方法

小结

dddsample-core定义了Entity、ValueObject、DomainEvent接口,它们分别定义了sameIdentityAs、sameValueAs、sameEventAs方法。

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当一个代码的工匠回首往事时,不因虚度年华而悔恨,也不因碌碌无为而羞愧,这样,当他老的时候,可以很自豪告诉世人,我曾经将代码注入生命去打造互联网的浪潮之巅,那是个很疯狂的时代,我在一波波的浪潮上留下了或重如泰山或轻如鸿毛的几笔。

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