向PouchDB文档添加其他附件

Question

I tried to add additional attachment to my document in PouchDB in my electron application. However I can only add last attachment and the old one is overwritten.

The following data is not amended in a way which add new file:

_attachments":{"someFile.jpg":{"content_type":"image/jpeg","revpos":5,"length":38718,"digest":"md5-X+MOUwdHmNeORSl6xdtZUg=="}

Should I read document first and recreate it adding additional file using multiple attachments with the following method:

db.put({
  _id: 'mydoc',
  _attachments: {
    'myattachment1.txt': {
      content_type: 'text/plain',
      data: blob1
    },
    'myattachment2.txt': {
      content_type: 'text/plain',
      data: blob2
    },
    'myattachment3.txt': {
      content_type: 'text/plain',
      data: blob3
    },
    // etc.
  }
}); 

?

Below you can see part of the code i try to run to check if i can add two attachments to one document (actually i try to use the same file twice to simplify test):

pdb.putAttachment(id, name, rev, file, type).then(function (result) {
                                                                              console.log("att saved:");
                                                                              console.log(result);
                                                                            }).catch(function (err) {
                                                                              console.log(err);
                                                                            });

var newFileName = "new" + name;
pdb.putAttachment(id, newFileName, rev, file, type).then(function (result) {
                                                                                  console.log("att saved 2:");
                                                                                  console.log(result);
                                                                                }).catch(function (err) {
                                                                                  console.log(err);
                                                                                });

The outcome is:

Object {ok: true, id: "1489351796004", rev: "28-a4c41eff6fbdde8a722a920c9d5a1390"}
id
:
"1489351796004"
ok
:
true
rev
:
"28-a4c41eff6fbdde8a722a920c9d5a1390"

CustomPouchError {status: 409, name: "conflict", message: "Document update conflict", error: true, id: "1489351796004"}
error
:
true
id
:
"1489351796004"
message
:
"Document update conflict"
name
:
"conflict"
status
:
409

It looks I don't understand something or I do not know how to use putAttachment properly.

I would also add what how data in sqlite looks like(by-sequence table, json row):

{...,"_attachments":{"testPicture.jpg":{"content_type":"image/jpeg","revpos":34,"length":357677,"digest":"md5-Bjqd6RHsvlCsDkBKe0r7bg=="}}}

The problem here is how to add another attachment to the structure. Somehow I cannot achive that via putAttachment

Answer 1

put replaces the document. If you want to add an attachment to an existing document without overwriting its contents you should use putAttachment .

Answer 2

Your question and especially the code are quite hard to read, so the error was not so easy to spot: You didn't wait for the promise to be resolved. When you update a document with revision 1, you have to wait for the results, read the revision from there, and only then write the second attachment. This would be my (untested) take on your code:

pdb.putAttachment(id, name, rev, file, type)
.then(function (result) {
  // Use the new revision here:
  return putAttachment(id, newFileName, result.rev, file, type);
}).then(function (result) {
  console.log(result);
}).catch(function (err) {
  console.log(err);
});

Adding two attachments at once is possible if you encode them correctly, but you're on your own with it. I'd recommend that you shouldn't do that – better use the abstractions that PouchDB provides.

Also don't analyze the underlying data structures too much, because depending on the storage adapter used the data storage might differ drastically. It's quite interesting how different adapters store their data, but never rely on anything you find out – data formats might change.