Best way to model Customer <--> Address

Question

Every Customer has a physical address and an optional mailing address. What is your preferred way to model this?

Option 1. Customer has fo

Answer 1

Good thread. I have spent a while contemplating the most suitable schema and I have concluded that quentin-starin's solution is the best except I have added start_date and end_date fields to what would be his PersonAddress table. I have also decided to add notes, active and deleted.

deleted is for soft delete functionality as I think I do not want to lose trace of previous addresses simply by deleting the record from the junction table. I think that is quite wise and something others may want to consider. If not done this way, it could be left to revision of paper or electronic documents to try to trace address information (something best avoided).

notes I think of being something of a requirement but that might just be preference. I've spent time in backfill exercises verifying addresses in databases and some addresses can be very vague (such as rural addresses) that I think it is very useful to at least allow notes about that address to be held in the record address.

One thing i would like to hear opinions on is the unique indexing of the address table (again, referring to the table of the same name in quentin-starin's example. Do you think it should be unique index should be enforced (as a compound index presumably across all not-null/required fields)? This would seem sensible but it might still be hard to stop duplicate data regardless as postal/zip codes are not always unique to a single property. Even if the country, province and city fields are populated from reference data (which they are in my model), spelling differences in the address lines may not match up. The only way to best avoid this might be to run one or a number of DB queries from the incoming form fields to see if a possible duplicate has been found. Another safety measure would be give the user the option of selecting from address in the database already linked to that person and use that to auto-populate. I think this might be a case where you can only be sensible and take precautions to stop duplication but just accept it can (and probably will) happen sooner or later.

The other very important aspect of this for me is future editing of the address table records. Lets say you have 2 people both listed at: -

11 Whatever Street Whatever City Z1P C0D3

Should it not be considered dangerous to allow the same address table record to be assigned to different entities (person, company)? Then let's say the user realises one of these people lives at 111 Whatever Street and there is a typo. If you change that address, it will change it for both of the entities. I would like to avoid that. My suggestion would be to have the model in the MVC (in my case, PHP Yii2) look for existing address records when a new address is being created known to be related to that customer (SELECT * FROM address INNER JOIN personaddress ON personaddress.address_id = address.id WHERE personaddress.person_id = {current person being edited ID}) and provide the user the option of using that record instead (as was essentially suggested above).

I feel linking the same address to multiple different entities is just asking for trouble as it might be a case of refusing later editing of the address record (impractical) or risking that the future editing of the record may corrupt data related to other entities outside of the one who's address record is being edited.

I would love to hear people's thoughts.