Serde Properties - Ignore Comma In Quotes

MIster jashon

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·

Oct 14, 2024

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How to Ignore Commas Inside Quotes When Using serde_json in Rust

When working with JSON data using the serde_json crate in Rust, you might encounter a situation where you need to parse JSON strings containing commas within quoted values. By default, serde_json treats all commas as field separators, leading to parsing errors if commas are present within quotes.

The Problem:

Consider the following JSON string:

{
  "name": "John Doe, PhD",
  "age": 30
}

If we try to deserialize this JSON string using serde_json::from_str, we will get an error because the comma within the "John Doe, PhD" string is interpreted as a field separator, leading to an invalid JSON structure.

The Solution: Using serde Properties

The serde crate, which serde_json relies on, provides a powerful mechanism for customizing serialization and deserialization. We can leverage this mechanism to tell serde_json to ignore commas within quotes.

Here's how to do it:

1. Define a Custom Deserializer:

   use serde::{Deserialize, Deserializer};
   
   #[derive(Debug, Deserialize)]
   struct Person {
       #[serde(deserialize_with = "parse_name")]
       name: String,
       age: u32,
   }
   
   fn parse_name<'de, D>(deserializer: D) -> Result
   where
       D: Deserializer<'de>,
   {
       let s: String = Deserialize::deserialize(deserializer)?;
       Ok(s)
   }
   
   fn main() {
       let json_str = r#"{"name": "John Doe, PhD", "age": 30}"#;
       let person: Person = serde_json::from_str(json_str).unwrap();
       println!("{:?}", person);
   }
   

   In this example, we define a custom deserializer function called parse_name. This function takes a Deserializer and converts the raw string into a String, effectively ignoring any commas within quotes.

2. Apply the Custom Deserializer:

   We use the #[serde(deserialize_with = "parse_name")] attribute on the name field of our Person struct to apply our custom deserializer. This tells serde_json to use the parse_name function when deserializing the name field.

3. Deserialize the JSON:

   The serde_json::from_str function will now correctly deserialize the JSON string, recognizing the comma within the quotes as part of the name field.

Key Points:

• Ignoring commas within quotes: The custom deserializer avoids treating commas within quotes as field separators, allowing for accurate parsing.
• Flexibility: You can apply this technique to any field that might contain commas within quoted values.

Example with Multiple Fields:

use serde::{Deserialize, Deserializer};

#[derive(Debug, Deserialize)]
struct Data {
    #[serde(deserialize_with = "parse_string")]
    field1: String,
    #[serde(deserialize_with = "parse_string")]
    field2: String,
}

fn parse_string<'de, D>(deserializer: D) -> Result
where
    D: Deserializer<'de>,
{
    let s: String = Deserialize::deserialize(deserializer)?;
    Ok(s)
}

fn main() {
    let json_str = r#"{"field1": "value1, value2", "field2": "value3, value4"}"#;
    let data: Data = serde_json::from_str(json_str).unwrap();
    println!("{:?}", data);
}

In this example, we apply the parse_string deserializer to both field1 and field2, ensuring that commas within the quoted values are ignored during deserialization.

Conclusion:

By leveraging custom deserializers in serde, you can overcome the challenge of parsing JSON strings containing commas within quoted values. This technique provides flexibility and control over the deserialization process, allowing you to handle various JSON data structures effectively.

Remember: This approach is specifically for handling commas within quoted values and does not change the default behavior of serde_json for parsing other JSON elements.