mirror of
https://github.com/Luzifer/cloudkeys-go.git
synced 2024-11-15 09:22:19 +00:00
49 lines
2.1 KiB
Go
49 lines
2.1 KiB
Go
|
/*
|
||
|
|
Package expression provides types and functions to create Amazon 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 on.
|
||
|
|
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. Because 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 because 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.
|
||
|
|
*/
|
||
|
|
package expression
|