mirror of
https://github.com/Luzifer/cloudkeys-go.git
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49 lines
2.1 KiB
Go
49 lines
2.1 KiB
Go
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/*
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Package expression provides types and functions to create Amazon DynamoDB
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Expression strings, ExpressionAttributeNames maps, and ExpressionAttributeValues
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maps.
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Using the Package
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The package represents the various DynamoDB Expressions as structs named
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accordingly. For example, ConditionBuilder represents a DynamoDB Condition
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Expression, an UpdateBuilder represents a DynamoDB Update Expression, and so on.
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The following example shows a sample ConditionExpression and how to build an
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equilvalent ConditionBuilder
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// Let :a be an ExpressionAttributeValue representing the string "No One You
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// Know"
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condExpr := "Artist = :a"
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condBuilder := expression.Name("Artist").Equal(expression.Value("No One You Know"))
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In order to retrieve the formatted DynamoDB Expression strings, call the getter
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methods on the Expression struct. To create the Expression struct, call the
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Build() method on the Builder struct. Because some input structs, such as
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QueryInput, can have multiple DynamoDB Expressions, multiple structs
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representing various DynamoDB Expressions can be added to the Builder struct.
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The following example shows a generic usage of the whole package.
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filt := expression.Name("Artist").Equal(expression.Value("No One You Know"))
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proj := expression.NamesList(expression.Name("SongTitle"), expression.Name("AlbumTitle"))
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expr, err := expression.NewBuilder().WithFilter(filt).WithProjection(proj).Build()
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if err != nil {
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fmt.Println(err)
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}
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input := &dynamodb.ScanInput{
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ExpressionAttributeNames: expr.Names(),
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ExpressionAttributeValues: expr.Values(),
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FilterExpression: expr.Filter(),
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ProjectionExpression: expr.Projection(),
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TableName: aws.String("Music"),
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}
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The ExpressionAttributeNames and ExpressionAttributeValues member of the input
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struct must always be assigned when using the Expression struct because all item
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attribute names and values are aliased. That means that if the
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ExpressionAttributeNames and ExpressionAttributeValues member is not assigned
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with the corresponding Names() and Values() methods, the DynamoDB operation will
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run into a logic error.
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*/
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package expression
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