how can i use joins in mongodb ?

rahil shareef

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Jul 23, 2016, 5:11:19 PM7/23/16

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hi,

i am using latest mongodb 3.2.8 with c#.

i want to use joins .

kindly help me.

thank you

Senthil

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Jul 24, 2016, 4:21:02 PM7/24/16

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No joins in Mongo db. Mongodb provided flexibility to create relational in the single document to avoid joins unlike to create multiple tables with cross referenced in traditional RDBMS

William Hagan

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Jul 25, 2016, 3:29:37 PM7/25/16

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Do check out the $lookup stage of the aggregation operator to see if it addresses your need.

Cheers

Wan Bachtiar

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Jul 31, 2016, 11:18:46 PM7/31/16

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i am using latest mongodb 3.2.8 with c#. i want to use joins .

Hi rahil,

As mentioned by William, you can try the aggregation operator $lookup. The $lookup operator is available starting from MongoDB v3.2.

An example of C# $lookup snippet using MongoDB .Net driver, currently at version 2.2:

var query = from p in collection.AsQueryable()
            join o in otherCollection on p.Name equals o.Key into joined
            select new { p.Name, AgeSum: joined.Sum(x => x.Age) };

See mongo-csharp-driver $lookup LINQ for more information.

If you are requiring joins for a frequently used query in your application or use case, I would recommend to re-consider your data models/schema.
See also the following data modelling resources:

You may also be interested to know that the next session for free online course M101N: MongoDB for .Net Developers is starting tomorrow, 2nd of August. This course will go over schema design, querying, insertion of data, indexing and working with the C# driver.