Re: Database schema for "custom fields"

On 2024-09-10 12:08:14 +0500, Muhammad Usman Khan wrote:
> There is not a properly defined solution but you can try the
> Entity-Attribute-Value (EAV) Model. This is an alternative approach, where a
> separate table is used to store custom fields as attributes for each record.
> New fields can be added without altering the schema. There will be no need for
> DDL changes. There might be some cons as you might need multiple joins to
> retrieve all fields for a given record.

I think this is essentially Matthias' option 3:

> On Tue, 10 Sept 2024 at 11:57, Matthias Leisi <matthias(at)leisi(dot)net> wrote:
>
> I’m looking for input on a database design question. 
>
> Suppose you have an application that allows the user to add some kind of
> field to the application („custom fields“, „user defined fields“, „extended
> fields“, …), which could be of different types (eg string, int, bool, date,
> array of <any other type>, …), and which would have some additional
> properties (like a display name or description, or some access control
> flags).
[...]
> How would you design this from a DB point of view? I see a few options, but
> all have some drawbacks:
[...]
> 3) Use a „data table“ with one column per potential type (fieldid,
> valstring, valint, valbool, …). Drawback: complex to query, waste of
> storage? Pro: use all DB features on „true“ columns, but without needing
> DDL privileges.

> Are these the right drawbacks and pro arguments? Do you see other options?

I pretty much agree with your analysis. I used to use your option 3 a
lot, mostly because I thought that the schema should be fixed at design
time and not changed by the application. I'm less dogmatic now and would
probably lean more to your option 1 (let the application add columns to
an "extension table").

hp

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