Parsing YAML to check structure

Question

In a Symfony2 project I want to make a configuration file which gets loaded and gives indication, for each form field, if to display the field or not, and if making it required or not, depending on certain attributes of a "Project" entity.

parameters:
    fieldProperty:
        MyProfile:
            Name:
                Label: 'Your name'            
                ProjectType:
                    IT: 2
                    Non-It: 2
                    Hybrid: 2
                ProjectSize:
                    Small: 2
                    Medium: 2
                    Large: 2
                    Massive: 2
                ProjectComplexity:
                    Low: 2
                    Medium:  2
                    High: 2
                ProjectTimingUrgency:
                    Regular: 2
                    Urgent: 2
                    Mandatory: 2
                    Critical: 2
                    HighlyCritical: 2
                Sensitivity: 'none'
            Nickname:
                Label: 'Your nickname'            
                ProjectType:
                    IT: 0
                    Non-It: 0
                    Hybrid: 0
                ProjectSize:
                    Small: 0
                    Medium: 0
                    Large: 0
                    Massive: 0
                ProjectComplexity:
                    Low: 0
                    Medium:  0
                    High: 1
                ProjectTimingUrgency:
                    Regular: 0
                    Urgent: 0
                    Mandatory: 0
                    Critical: 0
                    HighlyCritical: 1
                Sensitivity: 'none'

I also use it to determine the form label of a given field. Considering that I have something like 2000 fields I'm thinking it would be elegant to make the attr section of the $builder->add of the formBuilder dynamic, so for instance if it's of type "textarea" then expect in the attr section the parameter rows that defines the number of rows. This means basically that I need to define a proper structure of the YAML document: if field A exists and is of type "whatever" then expect field B (and maybe even the possibility of specifying that if there is no field B then the default is "4") and so on.

I basically need a structured parser. Consider that the first "child" of the fieldProperty attribute is an entity name, so the parser doesn't have to expect a certain word there, just the string. Same story for the following child which is the field name (in the example below the entity is "myProfile" and the 2 fields are "Name" and "Nickname"). From that moment on the structure enters into play.

Is it doable in YAML or I have to switch to XML, which is a bit less human friendly?

Answer 1

You need to specify your structure in some way and Kwalify or some other schema validator can help with that.

There is however something you can do in YAML if you are familiar with programming. It is interesting is that your YAML file consists of basic scalars, mapping and sequences only, but your description seem to indicate that the mappings are more like objects that have (or should have) certain properties.

Using standard YAML tags you can indicate what kind of objects certain nodes represents, but to check values or existence of values would require you to have those objects in a program (I have done so with Python and the ruamel.yaml package¹, but other languages and parsers should work as well).

In addition you would need to add the tags by hand. If you can automate this tag assignment, by reading in the mapping/sequence tree and replacing nodes using some algorithm you don't need to tag, you can just run those assignments and then have the objects check the rules you specify for their classes. Adding tags in the source might confuse symfony2, in which case you would have to pre-process the (hand) tagged YAML before you can use it (often a safe-load and dump is enough for that).

There is a larger choice of tools to do this with XML. But you only need one tool, or one method like the one indicated above, that works for you. So I wouldn't give up on the readability of YAML just yet if I were you.

---

¹ _{Although my YAML round-trip package ruamel.yaml is open source (it is an enhanced version of PyYAML), the code where I verify YAML using objects unfortunately is not.}

Answer 2

Why just don't use the integrated Symfony TreeBuilders explained here:

https://symfony.com/doc/current/components/config/definition.html