使用MongoDB和PHP避免注入风险

I have this function and I want to change the function so that there is no risk of injection. The function retrieves the form information:

function retrieve(){

    if(isSet($_POST['text'])|| $_POST['text']==" ") return null;
    return $_POST['text'];
}

I think I found with htmlentities:

function retrieve(){

    if(isSet($_POST['text'])|| $_POST['text']==" ") return null;
    return htmlentities($_POST['text']);
}