Node.js更新文件中的JSON数据

Question

I have to write some JSON data on a file. Some JSON objects must be update during the execution of the program and these updates must be saved in the file (for example objects in array).

Exist a way to do this without rewrite the entire file?

JSON structure:

{
    "varA": {
        "varA1": value,
        "varA2": value,
    },
    "varB": value,
    "varC": value,
    "varD": value,
    "array": [
        { obj1 },
        { obj2 },
        { obj3 },
    ]
}

Answer 1

If you have more than one file, I would strongly encourage you to use MongoDB, as it is exactly what it is good for.

With MongoDB you can do things like (from docs ):

   db.books.update( { item: "Divine Comedy" },
             {
               $set: { price: 18 }, // set property value
               $inc: { stock: 5 },   // increment etc field value

             } )

   // add value in array
   db.bios.update(
     { _id: 1 },
     {
        $push: { awards: { award: "IBM Fellow", year: 1963, by: "IBM" } }
     }

)

UPDATE: Also, since you mentioned that files are in fact configuration, check out what Grunt can do. For instance answer to this question Updating file references in a json file via a grunt task

Answer 2

If you want slightly more sophisticated solution to file management (yet quite simple to implement), I'd:

1. create a new file instead of trying to rewrite an existing file (with a new filename every time). I'd suggest using something that includes a time stamp (either human readable or as milliseconds).
2. and always look for the newest file when loading/sync'ing the file
3. Purge the old files when you "find" a newer one and it reads successfully. If the file doesn't read successfully, something has happened. Fall back to the next file, and ideally delete the bad file. Or, just wait until a new file is successfully written.

This way, you don't need to worry about files not being completely written etc.