How to marshal a golang struct to JSON with custom field names?
In Go, if you want the structure field to use a custom field name when converting to JSON, you can implement it through the json tag of the structure field. 1. Use the json: "custom_name" tag to specify the key name of the field in JSON. For example, Name string json: "username"" will make the Name field output as "username"; 2. Add, omitempty can control the omitted output when the field is empty. For example, Email string json: "email,omitempty"" will not display the field when the Email is an empty string. Note that the "empty" judgment criteria for pointer type and numeric type are different; 3. For nested structures or anonymous fields, you can also use json tags to name it, such as structure field Address json:"address_info``` will output the content of the Address with "address_info" as the key, and the anonymous field can also be renamed through the tag. These methods cover most of the requirements of JSON serialization scenarios.
In Go, if you want the structure field to be converted to JSON, you only need to specify it using the json tag in the structure tag. This method is simple and direct, but there are several details that need attention.
Custom field names using json tag
Go's standard library encoding/json will automatically read the field's json tag when serializing the structure to determine the output key name. For example:
type User struct {
Name string `json:"username"`
Age int `json:"user_age"`
} In the example above, Name field will be named "username" when outputting JSON, and Age will be named "user_age" .
If you do not set the json tag, then by default, the JSON key name is the structure field name and is in lowercase the initial letter. For example, if the field is named Email , then the JSON output is "email" .
Control whether to omit empty value
Sometimes you may want certain fields not to be displayed in JSON when they are empty (such as empty strings, 0, nil, etc.). At this time, you can add ,omitempty to the json tag:
type User struct {
Name string `json:"username,omitempty"`
Email string `json:"email,omitempty"`
} This way, if Email is an empty string, it will not appear in the final JSON result.
Pay attention to the following points:
- If the field type is a pointer,
omitemptyis also supported. - For numeric types (such as
int), a value of0will also be ignored by omitempty, so be careful. - The criteria for "empty" judgment of different data types are slightly different, and it is necessary to judge whether it is applicable based on the actual situation.
Handle nested structures and anonymous fields
If your structure contains other structures or anonymous fields, you can also control the output field name through the tag.
For example:
type Address struct {
City string `json:"city"`
Zip string `json:"zip_code"`
}
type User struct {
Name string `json:"username"`
Address `json:"address_info"`
} In this example, the JSON name corresponding to Addr field is address_info , and the output effect is as follows:
{
"username": "tom",
"address_info": {
"city": "Shanghai",
"zip_code": "200000"
}
} If it is an anonymous structure field, the field name will be promoted to the outer structure by default. If you want to rename this embedded field, you can also use the json tag to specify the name.
summary
Basically that's it. Just remember a few key points: use json tags to customize the field name, combine omitempty to control the null value output, and pay attention to the handling of nested structures. These techniques can cover most of the needs in real scenarios.
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