Laravel dynamic where queries using Query Builder - php

Question

I am in new in Laravel. I want to make dynamic where queries with laravel query builder.Normally I can make dynamic queries in php
$where = array(
'hello' => 'world'
);
function get($where = null){
if($where == "") $where = "";
//Function which converts where clause into queries
wheretoqueries($where); //converts where clause
$sql = "SELECT * FROM $tbl $where";
return $sql;
}
echo get($where);
If where clause is null queries will be
SELECT * FROM $tbl
If where clause is not null queries will be
SELECT * FROM $tbl WHERE hello = "world"
Laravel orm works fine for where clause if key and value exists
A::where($where)->get();
If where is null following method will not work

Answer 1

You can chain the where queries as:
$query = Model::query();
if (!empty($value)) {
$query->where('column', $value);
}
$query->get();
OR
You can use when method as:
Model::when($value, function ($query) use ($value) {
return $query->where('column', $value);
})
->get();

Answer 2

Try this. If $where variable contain something then the query will execute otherwise it will retrieve all data from A Model.
function get($where = null){
if($where != null){
A::where('field_name', '=', $where)->first();
}else{
A::all();
}
}
Note: if your query return more than one value then you have to use get() method at end of query builder instead of first();
Reference: https://laravel.com/docs/5.3/queries#where-clauses