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  • Dec 04 15:45
    mukeshpiplai edited #1891
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Martin Vseticka
@MartyIX
I see, thank you for your answer! Thanks for you work on LiteDB!
Mi.Chi
@AlessioMiky76_twitter
Hi, this query works fine "select $.Car.doc0.name from TestQuery". It returns the value of name, doc0 is a sub document inside subdocument Car. How can i modifiy query to select all subdocuments inside Car and not only doc0 and get the values of name of all those subdocuments?
Mi.Chi
@AlessioMiky76_twitter
I've tried SELECT $.Car[*].name FROM TestQuery. No error are raised but result is empty. There are 8 subdocuments in Car with a [name] field
raizam
@raizam
hi, was litedb stress tested with a million items in a collection? does it scale?
also, is it possible to store items sorted using a timestamp?
Jbm
@JbMarchal_twitter
HI, I have a similar question :) Is LiteDB an in-memory database? When we perform a (read) query, is there any physical disk usage or is everything done in memory? Thanks for these informations ;)
Piet Eckhart
@pietsoftwaretogo
Hi, A week ago I've asked about the date for upcomming release on github: mbdavid/LiteDB#1810
Does anyone have an answer?
Leonardo Nascimento
@lbnascimento
@AlessioMiky76_twitter This sort of query (iterating through values in a document) is currently not supported. You would have to create some code that does it.
@AlessioMiky76_twitter I believe it could be supported with some small changes to the SQL parser, I'll look into it.
Leonardo Nascimento
@lbnascimento
@raizam There is a LiteDB.Benchmarks project in our solution, which can be use to measure performance. We ran some tests earlier this year, but I can't seem to find the results, sorry about that.
@raizam You can create an index over a DateTime field or even make it your Id field. Due to the BSON spec, LiteDB only stores dates up to the miliseconds (losing a bit of precision). There is a simple workaround for that though, so let me know if you need help with that.
@JbMarchal_twitter LiteDB can be used as an in-memory database by using :memory: as its datafile or by using the LiteDatabase ctor that takes a Stream (you can pass a MemoryStream to it)
raizam
@raizam
thanks @lbnascimento

@raizam You can create an index over a DateTime field or even make it your Id field. Due to the BSON spec, LiteDB only stores dates up to the miliseconds (losing a bit of precision). There is a simple workaround for that though, so let me know if you need help with that.

will the DateTime order be preserved when I'll iterate the records? in both indexed/key scenarios?

Mi.Chi
@AlessioMiky76_twitter
@lbnascimento thanks, i cross fingers, it is a must to have feature ;)
Leonardo Nascimento
@lbnascimento
@raizam Yes, the order will be preserved.
raizam
@raizam
perfect :)
raizam
@raizam
is it possible to get a list of ids without fetching the collection?
Leonardo Nascimento
@lbnascimento
@raizam If you don't have an open LiteCollection, you can use the LiteDatabase.Execute(string command)
@raizam Something like db.Execute("select $._id from collection").ToList(). This will give you a list of BsonDocuments containing the id
@raizam If you wanted to do it all in one command, I would suggest var ids = db.Execute("select $._id from collection").ToEnumerable().Select(doc => doc["_id"].AsInt32).ToList(); (assuming the id is Int32)
raizam
@raizam
I see. I'm storing objects with large binary data, so retrieving BsonDocument would still allocate all the memory needed for the whole documents right?
I guess I should use DbRef
Leonardo Nascimento
@lbnascimento
@raizam Not exactly. LiteDB will still navigate through the documents in the collection (this is something we intend to optimize in future versions), but it will only deserialize the necessary fields.
martinweihrauch
@martinweihrauch
Hello everyone, I am using LiteDB, which I love because of the ease of use and quick deployment at customer's sites. I just have one question: I am using LiteDB for a self-written backup program für Azure blobs. Now, there is a situation, where I would like to "loop" through all database entries of one collection. I only found the possibility to load the entire collection as a List. Is there a possibility of a memory problem, if I have e. g. millions of records, which I want to loop through or do you have some way of caching? Thx
Leonardo Nascimento
@lbnascimento
@martinweihrauch Methods like LiteCollection<T>.Find(...) and LiteCollection<T>.FindAll() return an IEnumerable<T> and documents are only loaded when they're needed. So, you can simply use a foreach loop to iterate through this IEnumerable<T>.
@martinweihrauch However, if you call .ToList() or .ToArray(), then all the documents in the collection will be loaded into memory.
martinweihrauch
@martinweihrauch
@lbnascimento Oh God - thanks so much - not only did I learn how to handle that with LiteDB, but also learnt some more C# today because of you! BTW: are you financially backed somehow for your efforts?
travis-leith
@travis-leith
I've just encountered LiteDb for the first time. Looks cool. I am considering using it but want to check with more experienced users about when not to use it. My app currently has a small user base, but it could grow in the future. Is LiteDb recommended for apps with many concurrent users?
Hank G
@HankG
"Concurrent users" as in one process with many users or "concurrent users" as in multiple applications connecting to the same database?
travis-leith
@travis-leith
@HankG I can probably get away with one process many users for a while at least. Your comment led me to the docs on this topic. I see that one process is preferred if speed is a concern. Reading between the lines my take currently is that LiteDB is super simple and capable for a monolithic application (or at least single process access) that doesn't require horizontal scalability/high availability. Would you agree?
Hank G
@HankG
Think of it as SQLite but a NoSQL document database
the deployment use cases for the two are similar
travis-leith
@travis-leith
makes sense
raizam
@raizam
What is the cost of a new LiteDatabase("file") ? And what is the recommended life time for the LiteDatabase instance? would it be ok to keep it opened during the application lifetime?
Hank G
@HankG
I use it for the life of the application since it is the backbone of the persistence layer.
raizam
@raizam
thanks @HankG. in my case it's not a good idea because I'm accessing the data from multiple processes. most of the time they don't overlap, but I did get an exception when the db file was locked
Hank G
@HankG
Yeah anything with multiple processes I'm going to jump to Mongo for a Document database
or Postgres for relational
toumir
@toumir
@mbdavid Hi,
@lbnascimento explained well how LiteDB works under the hood,
Since I made a big refactor and all my queries are based on predicates, I am stuck for more than 3 weeks, can someone help me to find a solution for this situation,
Did someone manage how to combine two predicate and use it in LiteDB ?
thanks developers ---- issue: #1829
Chadley08
@Chadley08
Hello - We have a system where we need to persist large XML documents (~10-20MB each). I noticed that the document size limit is 1MB. Does this rule out LiteDB as a good choice for persistence?
Leonardo Nascimento
@lbnascimento
@Chadley08 This limit has been increased to 16MB recently. And LiteDB internally uses BSON, which is much more compact than XML or even JSON.
However, you still need to make sure that you won't ever need to store files that use more than 16MB after BSON serialization.
Chadley08
@Chadley08
@lbnascimento Thank you! After reviewing the docs a bit more, it looks like I can deserialize my XML file to a domain object, then I'm going to try saving that to the LiteDB as I think it will create a document for each object in the object's hierarchy. Those should be relatively small.
Torben Stallknecht
@stallemanden
It might be, that my Googling and reading abilities are crap, but I have been unable to find the answer. What, if any, limit is there to the database. I get that Documents are 1MB(16MB in newer versions?). There is a limit of 8000 bytes for collection names, which in essens limits the amount of collections. So, let's say I have 1 collection in my database. How many 1 MB documents can it store?
Leonardo Nascimento
@lbnascimento
@stallemanden There's no limit for number of documents in a collection.
SKProCH
@SKProCH_gitlab
Hello. My TimeSpan? store as {"$numberLong":"600000000"}, but when i try deserialize them i get exception: cant cast long to TimeSpan. But if i use non-nullable TimeSpan all is ok. What am I doing wrong?
Leonardo Nascimento
@lbnascimento
@SKProCH_gitlab What version of LiteDB are you using?
Chadley08
@Chadley08

Is it possible to use the following expression with LiteDB?

return maintenanceAssetCollection.UpdateMany(_ =>
            new MaintainableAssetEntity()
            {
                AttributeDatumEntities = new List<IAttributeDatumEntity>(),
                Id = _.Id,
                LocationEntity = _.LocationEntity,
                NetworkId = _.NetworkId
            },
            _ => _.NetworkId == networkId);

I keep getting a runtime NotSupported exception. When I change the list assignment to null it works.

Ah, I changed the code to this and it seemed to work:

return maintenanceAssetCollection.UpdateMany(_ =>
            new MaintainableAssetEntity()
            {
                AttributeDatumEntities = new List<IAttributeDatumEntity>() { },
                Id = _.Id,
                LocationEntity = _.LocationEntity,
                NetworkId = _.NetworkId
            },
            _ => _.NetworkId == networkId);

Note the curly brackets in the new list expression are the change.