How to process json data in php

Json in PHP is usually a very common thing for some experienced developers. When processing json data in PHP, you often need to use some operations on arrays, such as processing key-value pairs. However, sometimes, we encounter such a situation: processing a non-array structure of json data, so how do we specify the key?

Let’s first take a look at some basics of processing json data in PHP.

Processing json in PHP is usually divided into two directions: converting PHP arrays into json strings, and converting json strings into PHP arrays.

First, let’s take a look at the conversion of arrays to json. In PHP, there is a very useful function json_encode that can convert a PHP array into a json format string.

For example, suppose we have the following array:

$arr = array("name" => "Tom", "age" => 28, "gender" => "male");

If we want to convert this array into json, we can write like this:

$jsonStr = json_encode($arr);
echo $jsonStr;

Output result:

{"name":"Tom","age":28,"gender":"male"}

You can see here that the original PHP array has been successfully converted into a json format string. At the same time, you can also see that JSON data is a key-value pair structure.

Next, let’s take a look at the situation of converting json to array. In PHP, there is a very useful function json_decode that can convert a json format string into a PHP array.

For example, suppose we have the following json data (assuming we save the json string generated in the previous example into the file data.json):

{"name":"Tom","age":28,"gender":"male"}

If We want to read this json data and convert it into a PHP array. We can write it like this:

$jsonStr = file_get_contents("data.json");
$arr = json_decode($jsonStr, true);
var_dump($arr);

Output result:

array(3) {
    ["name"] => string(3) "Tom"
    ["age"] => int(28)
    ["gender"] => string(4) "male"
}

You can see that the original json format string has been successfully converted into PHP array.

Furthermore, if we only need to retrieve one of the values, we usually use a method similar to the following to retrieve the corresponding value using the key of the array:

echo $arr['name']; // 输出 Tom

However, we return to The first question raised: Assume that the json data structure we read is as follows:

{
    "status":1,
    "data":{
        "name":"Tom",
        "age":28,
        "gender":"male"
    }
}

At this time, if we want to take out the name value, what will we do?

Usually, we will think of the following code:

$jsonStr = file_get_contents("data.json");
$arr = json_decode($jsonStr, true);
echo $arr['data']['name'];

However, such a code will cause a Notice error:

Notice: Undefined index: data in ...

This is because PHP thinks $arr is an array, but we try to access data like an array in JSON data, and it will be recognized. as a string rather than an array.

In order to solve this problem, we need to use $arr->data->name to specify the key:

$jsonStr = file_get_contents("data.json");
$obj = json_decode($jsonStr);
echo $obj->data->name;

This way we can correctly output: Tom. Here, note that the object we create is of type stdClass, not an array type, so we need to use $obj->data->name to specify the key.

To summarize, when we process JSON data with non-array structure, we need to use objects instead of arrays. At the same time, we can also use this method to traverse non-array structured JSON data.

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