Handling multi-value attributes in JPA Map Storage #9638

ahus1 · 2022-01-19T12:06:11Z

ahus1
Jan 19, 2022
Collaborator

Problem statement

Map Storage currently supports multi-valued attributes, see

public interface EntityWithAttributes {
    Map<String, List<String>> getAttributes();
    /* ... */
}

As this interface uses List, this implies three behaviors:

Lists are "ordered", so they preserve the order of the elements inserted, and you can insert elements at specific positions
Two items that are "equal" can appear multiple times in the list
When retrieving a previous stored entity from a store, the order of the list needs to be preserved

The current JPA storage implementation deviates from these behaviors:

JpaClientEntity defines a Set for the attributes, thereby preventing duplicates and not preserving the order

Approach

Change the JPA implementation to store an ordered list:

enhance the database to add a column that represents the position of the item in the list, so the order can be restored later
change the Set to a List in JpaClientEntity

Benefits

JPA store will retrieve the attribute in the order they have been stored.

Alternatives

Leave it "as is".
Change the EntityWithAttributes that values are stored as a Set and not a List

ahus1 · 2022-01-20T14:00:16Z

ahus1
Jan 20, 2022
Collaborator Author

Summary of the discussion with the team:

In the case of an address it could make sense to have a multi-value ordered list, as the order of the address lines need to be preserved for the address to be correct. Therefore the interface is correct in defining Map<String, List<String>>.

Therefore the JPA implementation should be changed to support a List instead of a Set, thereby preserving the order and allowing for multiple identical entries.

Most likely a new column in the table client_attribute will be needed that preserves the ordering. Normalizing the datamodel for the 1:n relationship of keys and values will not be done to keep the data model simpler and faster.

Action items for @ahus1:

create a GitHub issue to update the JPA implementation to use a List instead of a Map

1 reply

ahus1 Jan 21, 2022
Collaborator Author

Issue created: #9712

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Handling multi-value attributes in JPA Map Storage #9638

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Handling multi-value attributes in JPA Map Storage #9638

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ahus1 Jan 19, 2022 Collaborator

Problem statement

Approach

Benefits

Alternatives

Replies: 1 comment · 1 reply

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ahus1 Jan 20, 2022 Collaborator Author

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ahus1 Jan 21, 2022 Collaborator Author

ahus1
Jan 19, 2022
Collaborator

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ahus1
Jan 20, 2022
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ahus1 Jan 21, 2022
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