-- import "github.com/aws/aws-sdk-go/service/dynamodb/expression"

Package expression provides types and functions to create DynamoDB Expression strings, ExpressionAttributeNames maps, and ExpressionAttributeValues maps.

Using the Package

The package represents the various DynamoDB Expressions as structs named accordingly. For example, ConditionBuilder represents a DynamoDB Condition Expression, an UpdateBuilder represents a DynamoDB Update Expression, and so forth. The following example shows a sample ConditionExpression and how to build an equilvalent ConditionBuilder

// Let :a be an ExpressionAttributeValue representing the string "No One You
// Know"
condExpr := "Artist = :a"
condBuilder := expression.Name("Artist").Equal(expression.Value("No One You Know"))

In order to retrieve the formatted DynamoDB Expression strings, call the getter methods on the Expression struct. To create the Expression struct, call the Build() method on the Builder struct. Since some input structs, such as QueryInput, can have multiple DynamoDB Expressions, multiple structs representing various DynamoDB Expressions can be added to the Builder struct. The following example shows a generic usage of the whole package.

filt := expression.Name("Artist").Equal(expression.Value("No One You Know"))
proj := expression.NamesList(expression.Name("SongTitle"), expression.Name("AlbumTitle"))
expr, err := expression.NewBuilder().WithFilter(filt).WithProjection(proj).Build()
if err != nil {
  fmt.Println(err)
}

input := &dynamodb.ScanInput{
  ExpressionAttributeNames:  expr.Names(),
  ExpressionAttributeValues: expr.Values(),
  FilterExpression:          expr.Filter(),
  ProjectionExpression:      expr.Projection(),
  TableName:                 aws.String("Music"),
}

The ExpressionAttributeNames and ExpressionAttributeValues member of the input struct must always be assigned when using the Expression struct since all item attribute names and values are aliased. That means that if the ExpressionAttributeNames and ExpressionAttributeValues member is not assigned with the corresponding Names() and Values() methods, the DynamoDB operation will run into a logic error.