Litedb: How to find the max _id or most recently updated object in collection

[chucksullivancvs]

__How to find the max _id or most recently updated object in collection?__

I'm kind of new to LiteDB.

Got most things working. I can create a POCO, make a db connection and do a collection.Insert().

Now I need to get the most recently added record so I can pull a value from it and increment it in a pattern.

I am struggling with using Queries and Expressions to find the MAX _id item in the collection.

Seems like this should be a pretty common problem but I can't find any examples.

Can someone help?

[nh43de]

I just had this problem yesterday

var latest = Coll.FindOne(Query.All(1));

Use -1 to get first item

where coll is your LiteCollection

let me know if that works for you

[mbdavid]

Hi guys,

First, your poco class will be updated with _id inserted.

Also, Insert method returns this number.

But, as @nh43de say, you can get lower (or highest) value in a index using this command:

var latest = Coll.FindOne(Query.All(Query.Asc));

[chucksullivancvs]

Hey Thanks!

I'm not used to people replying so quick and with such good options.

Both of these work:

var latest = collection.FindOne(Query.All(-1));
var latest = collection.FindOne(Query.All(Query.Descending));

Makes sense if you think of it as an object store and index rather than a database where you expect a simple MAX(col) function.

[nh43de]

Awesome! Glad it worked for you. Also @mbdavid - this is one of the coolest libraries I have come accross in several years. Thank you thank you for you hard work! This library is an amazing alternative to using a MongoDb backend for lightweight applications in .NET

[chucksullivancvs]

Agree Totally!

I've been using it now for just over a day and have already built an application using it. Great alternative to client-server SQL or NoSQL databases for some applications (like mine - a low use Windows Form application with just local storage needs).

[mbdavid]

Thanks guys! It's really nice to know about this. I'm still working v5 version that will the a biggest change in this project. In this case, you will resolve this using a single SQL query (or Linq query) like:

SELECT MAX(_id) FROM your_col
or
col.Query().Max(x => x.Id)

[MinChanSike]

As I see in LiteCollection.cs,

// Summary:
// Insert a new entity to this collection. Document Id must be a new value in collection
// - Returns document Id
public BsonValue Insert(T document);

int recentId = -1;
var docId = coll.Insert(info);
if (docId != null) recentId = docId .AsInt32;

@chucksullivancvs it's working for me.

[nh43de]

Thanks guys! It's really nice to know about this. I'm still working v5 version that will the a biggest change in this project. In this case, you will resolve this using a single SQL query (or Linq query) like:

SELECT MAX(_id) FROM your_col
or
col.Query().Max(x => x.Id)

That's really cool! Does this mean the IQueryable interface will be implemented?

[lbnascimento]

Hi! With the objective of organizing our issues, we are closing old unsolved issues. Please check the latest version of LiteDB and open a new issue if your problem/question/suggestion still applies. Thanks!