projections in grails

Projections in Grails

In Grails, projections are used to retrieve specific properties or calculated values from a domain class or a query result. Projections allow you to fetch only the data you need, which can improve performance and reduce memory usage.

To use projections in Grails, you can use the projections block in a criteria query or a named query. Here's an example:

def results = Book.createCriteria().list {
    projections {
        property('title')
        property('author')
    }
}

In the above example, we are using the projections block to specify that we only want to retrieve the title and author properties from the Book domain class.

You can also perform calculations or aggregations using projections. For example, you can calculate the average price of books:

def result = Book.createCriteria().get {
    projections {
        avg('price')
    }
}

In this case, we are using the avg projection to calculate the average price of books.

Projections can be used with both criteria queries and named queries in Grails. They provide a flexible way to retrieve specific data from domain classes or query results.