creating many to many relationship between documents in different lotus notes databases

Question

I am doing "traditional" lotus notes programming (same since R5) and need to implement linking between 2 document types (forms) residing in different databases.

Document of type (A) in database (A) can reference several documents of type (B) in database (B). And document (B) should also display its relationships with document (A), as document (B) can be related to different documents (A). We have Many to Many relationship.

At the moment it is implemented on one side only (one to many): Form of Document (A) contains embedded view of special "link" documents residing in database A. This link documents are created by lotusScript when user selects documents from database (B). When user clicks on an item in this embedded view, it opens document (B).

Client wants to be able to edit this relationship on any side, so that if he edits it in form (A), form (B) is updated. Form (B) is supposed to have the same kind of embedded view or a list of associated documents of type (A)

What is the best way to implement it?

Client's infrastracture is Lotus Domino 8.5.2 + Lotus Notes 8.5.2, so theoretically, composite applications approach may be an option.

The reason why I ask this question is that as far as I understand there is no good way in Notes to embed a view from another database. The requirement is that the database should be present on workspace to be displayed in some sort of dodgy list. It would be great to be able to specify target database for embedded view by server and replicaID, but instead we have a weird list of random workspace databases.

Answer 1

The main problem is that Notes wasn't designed to handle relationships like that between databases (nor anything besides parent child relationships for that matter). So the solution will have to be a creative one.

A couple of (off-the wall, potentially awful) ideas come to mind. One is to store the references in the documents themselves, and update them whenever the document is saved. That could all be done in LotusScript, and would require searching through the other database's documents to update their references.

Upside is that the performance when reading the documents would be excellent. There'd be no issues while reading Database A if Database B was unavailable. It keeps data local to each database. The downsides include the likelihood of save conflicts and the danger that references could get out of sync if documents aren't "saved" but instead are updated via agents, etc.

Another thought is to use agents to manage the links on a scheduled basis. If you don't need real-time up-to-date references, you could run an agent that scans Database B and updates the references in Database A. With this method you could choose either to update the Database A documents themselves - or - as it sounds like you've already done, create a set of link documents that show up in an embedded view. The latter eliminates the save conflict problem.

One more idea is to hide any references when you open a document in Database A, but provide a button to "show" or "update" references. When you click that button, it fires off LotusScript to search Database B and build a list on the fly. This would probably work quickly with less than 10,000 documents. That function could update the link documents you store on the same database which feed the embedded view.

Hope this helps!

Answer 2

What is the best way to implement it?

As you mention creating a composite application may allow you to do this, but would be restricted to windows rather then design level in the form.

eg.

[Window A] --- trigger ---> [Window B]

If you are not familiar with this system I did a tutorial which explains the basics.

http://www-10.lotus.com/ldd/compappwiki.nsf/dx/ibm-my-first-wire

Although the tutorial calls back to the same database, it is easy enough to point to a different one.

Personally I'd do it through XPages. I personally find it much easier to implement then through classic style notes design/comp apps. It will also allow you to display design elements within the same screen area.

Answer 3

As you've already heard, Lotus Notes has no referential integrity constraints built-in, you have to do it yourself.

I wouldn't be relying on document links as they're geared around UNID's which can change if you cut and paste the same document, thus losing the link. Try this,

1/ Create an "ID" field on each document. You can populate it by using @Unique in a computed field to generate an ID, and save that to the documents in both databases. You can create an agent to do this in lotusScript (LS), or formula. (Consider using the evaluate statement if doing in LS)

2/ Create a lookup view in each database that lists the documents by the new ID (don't forget to set the "sort order" of the ID column.

3/ Using an action button that can be configured for both databases, you can create a LS function that will open the the opposing databases view and return the ID field. (NotesUIWorkspace.pickliststrings would be the simplest way to pick the documents, otherwise you could build a dialogbox. Store the list of results in a field called "linkedID" as multi-value list.

4/ There may be more info that you want to store like document title or author, so you'll need to then get a handle to those documents using getdocumentbykey and then interrogating the fields you'll need to display information on screen.

5/ You can then also add a new field on the target documents you're referring to, call it "referrerID", which is a list of documents that reference the current document. This will maintain the two-way relationship.

The field that stores links must be a multi-valued field, otherwise it gets quite cumbersome to loop through list of linked document ID's and manage them.

This approach uses a static key so you can copy databases around without losing the relationships between documents the user has invested time in producing. You can (and probably will) lose those relationships if you rely on document universal ID's (described well in the @documentUniqueID documentation), if you cut and paste the document, or copy the database somewhere else they become new documents despite copying the same fields, and will be assigned a new universal ID, any document links for the old document will be invalid.

If the information you're displaying from the other database changes, you'll need to be able to refresh that data regularly, so consider writing a scheduled agent that can do the look up and refresh the relevant fields.

If the user intends to un-link or change the relationships between documents, then you'll need to add functions that loop through the key fields and keep the lists consistent with what the user is doing. So, like I said, Lotus Notes' flat data structure requires you manage all integrity constraints yourself.

If you want to get a little fancy you can use embedded views as they do support references from another database on the same server. Some tips about handling it in LotusScript here. And use an additional view that categorises your data by the referring ID. Embedded views are ok, as long as the view they're based on is not too big, otherwise it may affect the performance of the form that it is embedded into.