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A catalogue which is confugurable at the knowledge level to catalogue and organise any type of data and to provide structured access to it, free text querying of it and automatic data warehousing of events relating to it.

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/*
 * Copyright The Sett Ltd, 2005 to 2014.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.thesett.catalogue.model;

import java.io.Serializable;

/**
 * ExternalId defines an id type that is safe to pass to exernal systems because they are guaranteed to have a very long
 * life span and to not change or get issued to different data items.
 *
 * Items in the catalogue can map to a URL (or other externally nameable resource). Internally, items may have
 * database keys but these can and will change as items are deleted, merged, relegated and as the structure of the
 * database evolves. The sequences used to generate these surrogate keys may also be unique only within a single data
 * type and not across all data types. The idea behind external identifiers is that they will be unique across all
 * externally referenceable data types and that once issued they will live forever and never be re-issued for a
 * different item of data. When items are deleted permanently from the catalogue their external identifiers must be kept
 * to ensure that they are never re-issued.
 *
 * 

 * CRC Card Responsibilities
 * 
 Provide a long-lived identifier for a resource.
 * 
 *
 * @author Rupert Smith
 */
public class ExternalId implements Serializable
{
    /** Holds the UUID external id. */
    private String id;

    /** Holds the name of the resource class that this external id is for. */
    private String resource;

    /** Creates an uninitialized external id. */
    public ExternalId()
    {
    }

    /**
     * Creates an external id by id and resource name.
     *
     * @param id       The id.
     * @param resource The resource name or type.
     */
    public ExternalId(String id, String resource)
    {
        this.id = id;
        this.resource = resource;
    }

    /**
     * Gets the unique external id.
     *
     * @return The unique external id.
     */
    public String getId()
    {
        return id;
    }

    /**
     * Sets the unique external id.
     *
     * @param id The unique external id.
     */
    public void setId(String id)
    {
        this.id = id;
    }

    /**
     * Gets the resource that this is an external id for.
     *
     * @return The resource that this is an external id for.
     */
    public String getResource()
    {
        return resource;
    }

    /**
     * Sets the resource that this is an external id for.
     *
     * @param resource The resource that this is an external id for.
     */
    public void setResource(String resource)
    {
        this.resource = resource;
    }

    /**
     * Renders the external id as a string for debugging purposes.
     *
     * @return The external id as a string for debugging purposes.
     */
    public String toString()
    {
        return "id: " + id + ", resource: " + resource;
    }

    /**
     * Compares two external id's by their id values.
     *
     * @param  o The external id to compare to.
     *
     * @return true if they are equal by id.
     */
    public boolean equals(Object o)
    {
        if (this == o)
        {
            return true;
        }

        if (!(o instanceof ExternalId))
        {
            return false;
        }

        ExternalId externalId = (ExternalId) o;

        if ((id != null) ? (!id.equals(externalId.id)) : (externalId.id != null))
        {
            return false;
        }

        return true;
    }

    /**
     * Computes a hash code based on the id value only.
     *
     * @return A hash code based on the id value only.
     */
    public int hashCode()
    {
        return ((id != null) ? id.hashCode() : 0);
    }
}