A Way to Validate an Uploaded File Before Submitting

Question

I have discovered something and would like to share it with the community, while at the same time would like to know if this is "safe" to be used, or whether the slightest code change in Appian might cause it to misbehave. A way of validating the uploaded file before submitting it, like validation on extension, file size, file name...etc. When searching in the forum, the answer is: "it is not possible to be done without actually submitting the form and doing the checks after submitting." But I have found a way to get it to work, and below is the method: In the validation of the upload fileUploadField, call the object a!fileUploadField, passing the variable "value:ri!MainImage", assuming you are saving into "ri!MainImage" and then calling any properties like "uploadedDocumentName" as needed. This has worked for me perfectly. Below is a code snippet: a!fileUploadField( label: "Main Image", labelPosition: "ADJACENT", ... 
 
 OriginalPostID-153370 
 OriginalPostID-153370

Adel Ammari · Accepted Answer

...erseString has: =concat(char(reverse(code(ri!text)))) The use of reverse string is that sometimes a file might contain a . as part of its name, thus I am reading the file name in reverse. Looking forward to reading your comments.

Mike Schmitt · Answer

Everyone interested in this functionality, please reference the attached expression rule which should now handle the new 17.1 file upload field properties at the same time as the old rendering style. This rule accepts a rule input of type Document (ri!document), and will return a data dictionary consisting of 4 properties: "fullName" (name.ext), "name" (just name without extension, if any), "ext" (just extension, if any), and "size" (text-based abbreviated filesize - i.e. "44 kb", "2 mb", etc). The four properties are returned blank if no input or invalid input is passed, to ensure it's safe to use even when no file is uploaded yet. I've tested this in 17.1 (in an actual task form) as well as in interface designer in 17.1 and 16.3, and it seems to work as desired, though any feedback is welcomed. 
 [removed download - newer version in subsequent comment ]

Mike Schmitt · Answer

Attaching an updated version - this one will better handle irregularly-named files such as "noExtension" or ".properties" - both versions of the evaluation will now work for both of these scenarios (i.e. files with no extension or *only* an extension). [To anyone subscribed to this thread, sorry for the barrage of emails this is probably causing - i hope some are finding this useful at least.] 
 New File Upload Properties Rule.sail

Peter Lewis · Answer

Since it looks like someone recently asked this question again, the behavior listed in this discussion thread is not supported. In 17.2, a new version of the File Upload component was released where you can validate on file size, extension, and name using fv!files in the validations field. Please see the documentation for the File Upload field for more information and several examples of validations: 
 https://docs.appian.com/suite/help/latest/File_Upload_Component.html

sayalip · Answer

Well, I found a solution to my problem! 
 I replaced the new fileUpload version with 17.1 version and it worked just fine.