How to find two substrings in a field at the beginning and the end of an array-element in MongoDB?

Question

I have a collection in MongoDB which looks like this:

{
    "_id" : "ABCDEFGHIJK",
    "content" : {
        "arrayElements" : [ 
            "BD-cacf99afd87bd536da0162b2246f415e_FH",
            "BD-zhdfcf0bqa12qfT7jl10p9b3276o123p_HUCL",
            "WPG-bklcf10bqa12qg64jl99p9b3276o576a_HUCL",
            "EC-tzlscq10bqa12qg64jl19p9b3475o5z7_FH"
        ],
...
  }
}

Additionally, I have two variables (SessionVariables). One of them could contain the first part of the above elements (the part before "-") and the other one could hold the last part (part after the character "_"). For example:

Session.set('firstPart', "BD");
Session.set('lastPart', "FH");

Now, I would like to perform a query with findOne, which tells me whether any of the above elements contains Session.get('firstPart') at the first part until the character "-" AND Session.get('lastPart') after the character "_" . If this is true, than please console.log('One element contains both parts') .

I thought about $regex , but don´t know the right syntax. I need something like this:

if (collection.findOne({
      '_id': ABCDEFGHIJK), arrayElements: {
      $regex: /Session.get('firstPart')/ (AND) /
        Session.get('lastPart') / (IN ONE ELEMENT)
    }
  })) {
  console.log('One element contains both parts')
} else {
  console.log('None of the elements contains both parts')
}

In this case, where the first variable holds "BD" and the second one holds "FH", the output should be console.log('One element contains both parts') .

Answer 1

Try this:

...{"arrayElements": {$regex:val}...

Declare the string val beforehand as firstpart+"-.*_"+lastpart . You didn't clarify if your two variables have the - and _ in them, so I assumed they don't.