Retrieve Data
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Overview
In this guide, you can learn how to use the Kotlin Sync driver to retrieve data from a
MongoDB collection by using read operations. You can call the find() method to
retrieve documents that match a set of criteria specified in a query filter.
Sample Data
The examples in this guide use the restaurants collection in the sample_restaurants
database from the Atlas sample datasets. To learn how to create a
free MongoDB Atlas cluster and load the sample datasets, see the
Get Started with Atlas guide.
The documents in this collection are modeled by the following Kotlin data class:
data class Restaurant( val name: String, val cuisine: String )
Find Documents
The find() method retrieves documents from a collection. This
method takes a query filter and returns all matching documents. A query filter is a
document that specifies the criteria that the driver uses to match documents from the
collection.
To learn more about query filters, see the Specify a Query guide.
Find Documents Example
The following example uses the find() method to find all documents in which the
value of the cuisine field is "Spanish":
val results = collection.find(eq(Restaurant::cuisine.name, "Spanish"))
The find() operation in the preceding example returns a FindIterable object,
which you can iterate through by using the forEach() method, as shown in the following
example:
val results = collection.find(eq(Restaurant::cuisine.name, "Spanish")) results.forEach { result -> println(result) }
Restaurant(name=Tropicoso Club, cuisine=Spanish) Restaurant(name=Beso, cuisine=Spanish) Restaurant(name=Sabor Latino Restaurant, cuisine=Spanish) ...
Note
Find All Documents
To find all documents in a collection, pass an empty filter to the find() method:
val results = collection.find()
Modify Find Behavior
You can modify the behavior of the find() method by chaining methods to
the find() method call. The following table describes commonly used methods used for
modifying queries:
Method | Description |
|---|---|
batchSize() | Limits the number of documents to return per batch. To learn more about
batch size, see cursor.batchSize()
in the MongoDB Server manual. |
collation() | Sets the collation options for the query. |
comment() | Specifies a string to attach to the query. This can help you trace and interpret the
operation in the server logs and in profile data. To learn more about query comments,
see $comment in the MongoDB Server
manual. |
hint() | Specifies the index to use for the query. |
limit() | Limits the number of documents to be returned from the query. |
maxTime() | Sets the maximum execution time on the server for this operation. |
skip() | Sets the number of documents to skip. |
sort() | Defines the sort criteria to apply to the query. |
The following example chains the limit() and maxTime() methods to limit the
number of documents returned by the query to 10 and set a maximum execution time of
10000 milliseconds on the operation:
val results = collection .find(eq(Restaurant::cuisine.name, "Spanish")) .limit(10) .maxTime(10000)
For a full list of methods that modify the behavior of find(), see the API documentation
for the FindIterable class.
Additional Information
To learn more about query filters, see Specify a Query.
To view runnable code examples that retrieve documents by using the Kotlin Sync driver, see Read Data from MongoDB.
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: