How to build a Apex Class to handle a JSON format in my example

Question

I want to build a custom sync framework and combine serval object's data to a Json string. For example

List<Account> accounts = [select Id, Name, ... from Account where ...]; 

The sOBject is dynamic, it can be Account, Contact or CustomObject__c and the fields is also dynamic. the field between select and from clause is flexible. That means I don't know there will be how many fields. I want to convert the select result to this format:

   {
   "records": [
    {
        "values": [
            "00190000014IoCoAAK | 00081 | Super Mart | ...",
            "00190000014EoCAABK | 00082 | Test Mart | ...",
        ],
        "objName": "Account",
        "fields": "Id,AccountNumber,Name, ..."
    },
    {
        "values": [
            "0039000001JDBt7AAH | 00190000014IoCoAAK | Ues1 | ..."
        ],
        "objName": "Contact",
        "fields": "Id,AccountId,Name, ..."
    }
 ] 
}

How can I build a Apex calss to handle this Json?

Answer 1

Here is the sort of code I would write for this:

public class Records {

    public Record[] records;

    public Records() {
        records = new Record[] {};
        records.add(new Record(Account.SObjectType, new SObjectField[] {
                Account.Id,
                Account.Name,
                ...
                }));
        records.add(new Record(Contact.SObjectType, new SObjectField[] {
                Contact.Id,
                Contact.AccountId,
                Contact.Name,
                ...
                }));
    }

    public String toJsonString() {
        return JSON.serializePretty(this);
    }
}

public class Record {

    public String objName;
    public String fields;
    public String[] values;

    public Record(SObject sob, SObjectType type, SObjectField[] fields) {

        objName = String.valueOf(type);

        String[] names = new String[] {};
        for (SObjectField field : fields) {
            names.add(String.valueOf(field));
        }
        fields = String.join(names, ',');

        for (SObject sob : Database.query(''
                + ' select ' + fields
                + ' from ' + objName
                + ' ...'
                )) {
            String[] rowValues = new String[] {};
            for (SObjectField field : fields) {
                rowValues.add(String.valueOf(sob.get(field)));
            }
            values.add(String.join(rowValues, ' | '));
        }
    }
}

where the string would be created using:

String jsonString = new Records().toJsonString();

The custom formatting is handled by Apex code and then the standard serialize method handles the standard JSON conversion.