使用PHP从json文件中读取第一条记录

Question

I have json file having content like this :

[{
    "name" : "Mak",
    "registration_code" : "Registration code",
    "date" :"date",
    "time" : "time",
    "file_data" :{
        "Feature_0" : "0,0.956222737454317,"
    }
  },
  {
    "name" : "Andy",
    "date" :"date",
    "time" : "time",
    "file_data" :{
        "Feature_0" : "0,0.956222737454317, "
    }
  }]

Right now to read first record i am using file_get_contents get complete data and then parsing into array. I want to fetch only first record without getting whole file content in memory using php. Is there any way to do this ?

Many Thanks, M.

Answer 1

This is a hack but if you know the JSON structure. Anyway }, may not occur in the first record.

$first = explode("},", $json_string, 2)[0];
$first .= "}]";
$obj = json_decode($first)[0];

If you do not want to read the whole JSON file you could do something like this (adjust to your needs!):

         $content = "";
         $handle = fopen("json.file", "r"); if ($handle) {
         while (($line = fgets($handle)) !== false) {

                // with nested objects you have to count the occurrences of { and make sure it is the closer for the first object
                if (strpos($line, '},') !== false) {
                    break;
                } else {
                    $content .= $line;
                }
           }

           fclose($handle); 
        }  // proceed only with the lines read ...
        $content .= "}]";
        $obj = json_decode($content)[0];

Anway everything which I just suggested here is usually not recommendable (in 99% of the use cases) . Maybe you have to adapt this code a bit and also it will not work for minified JSON.

Better you parse the whole file and go ahead.