How to extract field values ​​from nested JSON data (two-dimensional map) safely and efficiently?

Securely extract field values ​​from nested JSON data (two-dimensional map)

When processing JSON data, you often encounter nested structures, especially two-dimensional maps. This article describes how to safely extract the values ​​of a specific field from a 2D map and avoid type assertion errors.

Suppose jmap is a map after parsing JSON data received from the network. The goal is to get username field value from the submap jmap["user"] . Direct type conversion can cause an error because the actual type of jmap["user"] is map[string]interface{} , not map[string]string .

Converting user directly to map[string]string will cause the type assertion to fail and raise panic. Even if converted to map[string]interface{} , the username value cannot be accessed directly because it is still of type interface{} .

Solution: Step by step type assertion

In order to securely obtain username value, two type assertions are required:

1. Assert user as map[string]interface{} to access username field.
2. Gets the value of username field and assert it as string type.

The correct code is as follows:

 usernameTmp := user.(map[string]interface{})["username"].(string)

This code first converts user to map[string]interface{} , then accesses the username field, and finally converts the value of the field to string type, safely assigning the value to the usernameTmp variable. This method effectively avoids type conversion errors and ensures that field values ​​are safely extracted from 2D maps.

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