Using couchbase for a POS iPap app

[ma...@elmalabarista.com]

I'm building a point of sale for iOS. I need a reliable sync history, because the app will work off-line or under bad internet connections, so the data could be 1 week behind the online data.

I read in http://docs.couchbase.com/couchbase-lite/cbl-concepts/ that this kind of app is supported. I have tried parse.com/firebase.com but their sync history is weak.

The app use sqlite internally, and I wish to not change this in this stage of the app (I'm close to beta). So I sync the data from/to couch.

The app is for small companies, each company have several sales devices. The data is shared among all the devices registered with the company, so the data must be in sync among all the devices of that company.

This are my questions:

- Exist a hosted version of couchbase that I can rely on? That was the reason behind choseparse.com. If not, how much servers I need to start? The data of each company is small (ie: few hundreds of customers and products, 1-200 invoices per day with related inventory).

- Is possible in a transaction to update multiples tables (like invoice header, invoice details, payment details)?

- Is possible to have a reliable sync if the device lost connection for several hours/days?

- When the data is updated in client A, is propagated to client B & C or I need to do polling?

- I update the data in sqlite and replicate it with couch. If the sync is not successfully, then is possible to retry it?

- The query language will be available soon in the iOS library?

- Is possible to monitor the sync? Like providing a progressbar?

- Is possible to know if the client is up-to-date with the server? Like for purge the couch data locally and start again clean...

- Exist a sample in integrate with sqlite?

[Jens Alfke]

On Dec 12, 2013, at 2:19 PM, ma...@elmalabarista.com wrote:

> - Exist a hosted version of couchbase that I can rely on? That was the reason behind choseparse.com. If not, how much servers I need to start? The data of each company is small (ie: few hundreds of customers and products, 1-200 invoices per day with related inventory).

There’s an experimental hosted service at http://couchbasecloud.com but you shouldn’t use it for a real product. There may be more serious hosting services coming, but we can’t comment on that.

You should be able to run on a single server. We have an AWS configuration that’s easy to set up, but I’m not sure exactly how to get ahold of it.

> - Is possible in a transaction to update multiples tables (like invoice header, invoice details, payment details)?

Usually you store all related documents in a single database, even if in a relational database they’d be in different tables. It’s common to use a “type” property to distinguish between different types of documents.

You can update multiple documents at once using the database’s -inTransaction method.

> - Is possible to have a reliable sync if the device lost connection for several hours/days?

Yes.

> - When the data is updated in client A, is propagated to client B & C or I need to do polling?

If B and C have active ‘pull’ replications, they’ll receive the change in a second or two.

> - I update the data in sqlite and replicate it with couch. If the sync is not successfully, then is possible to retry it?

Once you’ve updated documents in Couchbase Lite, and set up a replication, it’ll keep trying to replicate them until it succeeds.

> - The query language will be available soon in the iOS library?

Do you mean the experimental query language (NiQL) being developed for Couchbase Server? We don’t have any plans to put that into Couchbase Lite yet.

> - Is possible to monitor the sync? Like providing a progressbar?

Yes, observe the notifications the CBLReplication posts.

> - Is possible to know if the client is up-to-date with the server? Like for purge the couch data locally and start again clean...

Yes, when the replication’s status changes to ‘idle’ that means everything is up to date.

> - Exist a sample in integrate with sqlite?

Not that I know of.

—Jens

[ma...@elmalabarista.com]

OK, sound good.

I have a last question. The sync need to be in a specific order. I can't sync InvoiceDetail if I don't have finished InvoiceHeader - Customers - Products 

So I need to process this in this order: 1-Products, 2-Customers, 3-Invoice-4Details

How can be done?

[Jens Alfke]

In general it can't. Replication syncs individual documents, with no guarantees about ordering. What you’re asking for is basically transactions, but transactions can’t be made to work reliably in a loosely-distributed system like this (if you want the theory, it’s because of the CAP Theorem — we’re sacrificing some Consistency to get Availability and Partition-resistance.)

Most of the time things will work because the replicator sends changes in the order in which they were made. But you can’t depend on this because every change is being downloaded asynchronously, so the order they’re inserted might not match.

You’ll need to code defensively so that, for example, if you receive an invoice that refers to a customer that doesn’t exist yet, you don’t crash but instead ignore it or wait for the customer document.

—Jens

[Shameel Abdulla]

Hi,

Did Couchbase work fine? Can you share any issues if you faced any