Converting SQL to JSON and keeping the null values? - php

Question

The issue:
I'm converting some SQL tables into JSON format and I have some null values which aren't being presented in the format I would like. When there's a null value in my table, it turns into " " when converted to JSON, but I want it to just say null instead of double quotation marks.
The code:
$conn = new mysqli($servername, $username, $password, $dbname);
$result = $conn->query("SELECT firstname, middlename, lastname FROM nametable");
$outp = "[";
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
if ($outp != "[") {$outp .= ",";}
$outp .= '{"firstname":"' . $rs["firstname"] . '",';
$outp .= '"middlename":"' . $rs["middlename"] . '",';
$outp .= '"lastname":"' . $rs["lastname"] . '"}';
}
$outp .="]";
$conn->close();
echo($outp);
The JSON format that I am getting:
[
{"firstname":"John", "middlename": "Timothy", "lastname":"Doe"} ,
{"firstname":"Mary", "middlename":"", "lastname":"Jane"}
]
The JSON format that I want: (the different part is the null after middlename)
[
{"firstname":"John", "middlename":"Timothy", "lastname":"Doe"} ,
{"firstname":"Mary", "middlename": null, "lastname":"Jane"}
]
Edit: I don't want this: (because null will be treated as a string)
[
{"firstname":"John", "middlename":"Timothy", "lastname":"Doe"} ,
{"firstname":"Mary", "middlename":"null", "lastname":"Jane"}
]
What I have tried:
I tried editing my query to
SELECT firstname, middlename, lastname
FROM nametable
WHERE (nametable->>'middlename') is null
but it gets buggy and won't run.
I've also tried
SELECT firstname, middlename, lastname
FROM nametable
FOR JSON AUTO, INCLUDE_NULL_VALUES
but it also won't run.
Final edit: I played around with everyone's suggestions and I made it work with an if/else statement in the middle:
$conn = new mysqli($servername, $username, $password, $dbname);
$result = $conn->query("SELECT firstname, middlename, lastname FROM nametable");
$outp = "[";
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
if ($outp != "[") {$outp .= ",";}
$outp .= '{"firstname":"' . $rs["firstname"] . '",';
if (is_null($rs['middlename']) == true)
$outp .= '"middlename":null,';
else
$outp .= '"middlename":"' . $rs["middlename"] . '",';
$outp .= '"lastname":"' . $rs["lastname"] . '"}';
}
$outp .="]";
$conn->close();
echo($outp);

Answer 1

Convert your null field to string if you want to want JSON to print NULL instead of blank
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
if ($outp != "[") {$outp .= ",";}
$outp .= '{"firstname":"'. $rs["firstname"] == null ?"null":$rs["firstname"]. '",';
$outp .= '"middlename":"'. $rs["middlename"] == null ?"null":$rs["middlename"]. '",';
$outp .= '"lastname":"'. $rs["lastname"] == null ?"null":$rs["lastname"]. '"}';
}

Answer 2

Since having null inside the database causes problem, why not store "null" string instead, and when creating the JSON format, use conditional operator to select the real null .This is a sample, how your code suppose look like:
$outp = "[";
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
if ($outp != "[") {$outp .= ",";}
$outp .= '{"firstname":"' . $rs["firstname"] == "null" ? null : $rs["firstname"].'",';
$outp .= '"middlename":"' . $rs["middlename"] == "null" ? null : $rs["middlename"].'",';
$outp .= '"lastname":"' . $rs["lastname"] == "null" ? null : $rs["lastname"].'"}';
}
$outp .="]";

Answer 3

Here is an example with some dummy data
$db_results = array(
array('fname'=>'john', 'lname'=>'doe', 'property'=>''),
array('fname'=>'john', 'lname'=>'doe', 'property'=>''),
array('fname'=>'john', 'lname'=>'doe', 'property'=>NULL)
);
$output='';
$rowStr = '';
foreach($db_results as $i=>$row) {
$rowStr="{";
$rowStr.= '"fname":'.((is_null($row['fname']) || empty($row['fname'])) ? 'null' : '"'.$row['fname'].'"');
$rowStr.= ',"lname":'.((is_null($row['lname']) || empty($row['lname'])) ? 'null' : '"'.$row['lname'].'"');
$rowStr.= ',"property":'.((is_null($row['property']) || empty($row['property'])) ? 'null' : '"'.$row['property'].'"');
$rowStr.='}'; //add a comma here when a condition is met
$output.= $rowStr;
}
echo '['.$output.']';