Gradle Configuration will be slightly different for Android implementations
Setting up your entities is covered in other tutorials. The same annotations apply to
Kotlin managed entities as it does Java.
Kotlin Query Builder
Kotlin Query Builder was added in version 2.0.0. Although you can use it with Java it was designed
to use a DSL like syntax within Kotlin. The QueryBuilder class provides a less verbose syntax
for querying Onyx Database. It can be used to query an embedded, remote, or in memory database using
The Query can be given commands to filter and define query definition with the following methods:
The following methods can be used to retrieve, aggregate, listen to, delete, or update data.
Kotlin Query Builder DSL syntax varies from the traditional Onyx Database syntax. The following
criteria infix methods can be used to define criteria. The criteria operators are mapped using the
Since Kotlin requires parenthesis around chained infix method invocations, the order of operations
must be grouped using parenthesis. The and and or infix methods should operate the
same as any standard SQL or DSL querying language.
The property names for the criteria are string values.
The IN and notIn methods require list values and cannot be used with varargs since Kotlin
does not support varargs for infix methods.
The equivalent Query Criteria in Onyx Database using Java would be
Select fields rather than a typed query
The select method is not required for building a query within the Kotlin DSL but, it can be used
to retrieve only desired fields.
Using Order By
Order By method is used to specify query sorting. The following methods are available to define sort
Using Group By
Group By method is used to group results to allow aggregation. The following methods can be used with
This is an example of using the Group By to group players by rushing yards:
The Kotlin DSL supports the following functions
The following would be an example of getting the leading rusher for NFL stats using the max function.
For more details on Query Functions and Group By read this tutorial.
The Kotlin Query Builder DSL has several methods to retrieve data. Using Kotlin, you can use the
inherent commands including list, lazy, and count. Alternatively, you can use the lambda friendly
methods forEach, map, first, firstOrNull.
Using the .lazy method will only load the references of the results. It is not until you
the item within the result set that the entity will be loaded.
First / First or Null
Limiting results can be done using the .limit and the .first method. The first method
can be used
either to retrieve the first result or, it can be used to define the first result to skip to if
you pass an int value into the method. Also note, the first() method will throw an exception
if results are not present. To avoid an exception use firstOrNull().
For each provides a lambda friendly way of iterating through results
The map method is used to aggregate results. It works the same as the map method within
Kotlin for a collection
The filter method is not optimized to define criteria and does not reduce query cardinality. It is
an additional tool for aggregating query results.
In order to update values, invoke the .update method.
Setting property values are done by specifying the property as a string and using the to infix
to instruct what value to set it to.
The set can either be invoked multiple times for multiple properties, or by passing in vararg set
Delete query is executed by invoking the delete method.
The limit and filtering methods that apply to the list also apply to delete and update
Listening for Changes
The following methods apply to Query listeners.
Query listeners can be either attached to a query upon execution or explicitly subscribed using the
listen method. In order to ensure listeners are not leaked, you should keep a handle on the original
Kotlin QueryBuilder object.
Below is an example of using an update listener. When finished, the stopListening method is
called to un-subscribe the listener.