MongoDB Notes

When using MongoDB to store files, we have 2 collections:
1. The place where MongoDB store the file metadata: store.files
2. Ans place where MongoDB store the file content: store.chunks

Depending on the size of the file, one entry in store.files can points to many entries in store.chunks. The bigger the file, the more entry you’ll encounter.

1
2
3
4
5
6
7
8
// Show all/ list all entries from store.files
db.getCollection('store.files').find({});

// Show only a particular entry from store.files
db.getCollection('store.files').find({ _id : ObjectId("5b02d232cbce1d07e08401c7")});

// The same can be used for store chunks.
db.getCollection('store.chunks').find({});

The metadata/fields in the store.files can be expanded during query runtime (not saved into the MongoDB, only displayed during runtime)

1
2
3
4
db.getCollection('store.files').aggregate([
    { $match: { _id : ObjectId("5b02d232cbce1d07e08401c7")} },
    { $addFields:{'key_reference':'1234'}}
]);

Or we do an update into store.files which will be saved into the MongoDB

1
db.getCollection('store.files').updateMany({ _id : ObjectId("5b02d232cbce1d07e08401c7")},{$set:{'key_reference':'1234'}});
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *

*


2 × = twelve

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>