Since FileMaker has increased the server capacity and continued to polish their WebDirect client, is there any valid/good reason not to develop an online store (front and back end), using FileMaker?
Well you would have to pay for connection licenses for every customer for one thing
if you intend to offer it as a service, ... unviable (prices of concurrent connections) FMW does not cover that implementation segment.
There are many good reasons not to do this - licensing, capacity/performance, browser compatibility, design limitations (can't really build a responsive design).
I might consider this for a highly specialized application where there are a very small number of potential users. Might make sense for example if you are selling very expensive, specialized, and customized products where no existing platform exists that meets the customization requirements, and where the website will only be visited by pre-qualified leads. You may be able to get around the licensing issues by having a site license.
Other than that I just see no reason for it. There are many pre-built e-commerce platforms available and many are very good at what they do, so why reinvent the wheel? Integrate with these platforms using ODBC or a web service/cURL.
I don't think current licensing allows for "anonymous" users connected via FMP, FMGo or WebDirect. With FLT licensing you need to pay one licence per user. For instance, if you have a solution installed in an office with ten people accessing, you need to buy /rent an FTL for 10 users, even if there is never going to be more than five of them accessing the server simultaneously. At least this is my understanding. So you wouldn't be able to use WD with "unregistered" users.
On the other hand, if you were expecting hundreds of simultaneous users you would need a pretty powerful (and therefore expensive) server since WD requests are processed on the server.
As Jason Wood say, you could integrate FM with an existing e-commerce platform. For instance Prestashop, that has a MySQL back end and could be integrated via ESS. Not sure how hard this would be though.
Having said that, we are currently developing an online store using PHP and FileMaker, and for us is great developing an online store with the data model and exact functionality we need. We wouldn't be able to do this online store the way we want it using an existing platform, so we are pleased with the result (hopefully we will make a couple of cents!).
Also, for CWP there is the FileMaker Server 16 Data API option, that we would love to use instead of PHP, but it's still a mystery how FMI is going to charge for it so we cannot consider it as an option yet.
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