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package org.babyfish.jimmer.sql.ast.mutation;

/**
 * If the current entity object has associated objects, 
 * and these associated objects have properties beyond just an id, 
 * then these associated objects will also be automatically saved.
 * 
 * The associations of an entity object can be divided into two types:
 * 
 * Associations based on foreign keys. 
 * These associated objects are saved before the current object.
 * Associations not based on foreign keys (
 * such as associations based on intermediate tables, one-to-many associations). 
 * These associated objects are saved after the current object.
 * 
 * 
 * This enumeration specifies how to cascade save the second type of associations.
 *
 * @see SaveMode
 */
public enum AssociatedSaveMode {

    /**
     * On the basis of {@link #MERGE}, perform dissociation processing for
     * associated objects that are no longer needed by the current entity.
     *
     * Note that this mode requires the associated object to have either an
     * {@link org.babyfish.jimmer.sql.Id} or {@link org.babyfish.jimmer.sql.Key} properties
     * otherwise an error will be reported.
     */
    REPLACE,

    /**
     * If the associated object exists, update it; otherwise, insert it.
     *
     * Note that this mode requires the associated object to have either an
     * {@link org.babyfish.jimmer.sql.Id} or {@link org.babyfish.jimmer.sql.Key} properties
     * otherwise an error will be reported.
     */
    MERGE,

    /**
     * Unconditionally insert the associated object. If the associated object already exists,
     * repeated insertion will result in an error.
     */
    APPEND,

    /**
     * It functions the same as {@link #REPLACE},
     * but has lower usage requirements and lower performance.
     *
     * {@link #REPLACE} uses the {@link org.babyfish.jimmer.sql.Id} or
     * {@link org.babyfish.jimmer.sql.Key} properties of the associated object to
     * cleverly compare the data structure in the database with the data structure
     * that the user is trying to save, finding the differences between the two.
     * It's similar to the `virtual DOM diff` in React in the web domain.
     *
     * The operation method is very simple, first clearing all old associated objects,
     * then reinserting new associated objects. The performance is not as good
     * as {@link #REPLACE} and may even cause event storms when using triggers.
     * However, it can accept associated objects that have neither
     * {@link org.babyfish.jimmer.sql.Id} nor {@link org.babyfish.jimmer.sql.Key}.
     *
     * Unless you really need to accept associated objects that have neither
     * {@link org.babyfish.jimmer.sql.Id} nor {@link org.babyfish.jimmer.sql.Key},
     * please do NOT use this mode.
     */
    VIOLENTLY_REPLACE
}