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package expression
import (
"strings"
)
// ProjectionBuilder represents Projection Expressions in DynamoDB.
// ProjectionBuilders are the building blocks of Builders.
// More Information at: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ProjectionExpressions.html
type ProjectionBuilder struct {
names []NameBuilder
}
// NamesList returns a ProjectionBuilder representing the list of item
// attribute names specified by the argument NameBuilders. The resulting
// ProjectionBuilder can be used as a part of other ProjectionBuilders or as an
// argument to the WithProjection() method for the Builder struct.
//
// Example:
//
// // projection represents the list of names {"foo", "bar"}
// projection := expression.NamesList(expression.Name("foo"), expression.Name("bar"))
//
// // Used in another Projection Expression
// anotherProjection := expression.AddNames(projection, expression.Name("baz"))
//
// // Used to make an Builder
// builder := expression.NewBuilder().WithProjection(anotherProjection)
//
// Expression Equivalent:
//
// expression.NamesList(expression.Name("foo"), expression.Name("bar"))
// "foo, bar"
func NamesList(nameBuilder NameBuilder, namesList ...NameBuilder) ProjectionBuilder {
namesList = append([]NameBuilder{nameBuilder}, namesList...)
return ProjectionBuilder{
names: namesList,
}
}
// NamesList returns a ProjectionBuilder representing the list of item
// attribute names specified by the argument NameBuilders. The resulting
// ProjectionBuilder can be used as a part of other ProjectionBuilders or as an
// argument to the WithProjection() method for the Builder struct.
//
// Example:
//
// // projection represents the list of names {"foo", "bar"}
// projection := expression.Name("foo").NamesList(expression.Name("bar"))
//
// // Used in another Projection Expression
// anotherProjection := expression.AddNames(projection, expression.Name("baz"))
// // Used to make an Builder
// builder := expression.NewBuilder().WithProjection(newProjection)
//
// Expression Equivalent:
//
// expression.Name("foo").NamesList(expression.Name("bar"))
// "foo, bar"
func (nb NameBuilder) NamesList(namesList ...NameBuilder) ProjectionBuilder {
return NamesList(nb, namesList...)
}
// AddNames returns a ProjectionBuilder representing the list of item
// attribute names equivalent to appending all of the argument item attribute
// names to the argument ProjectionBuilder. The resulting ProjectionBuilder can
// be used as a part of other ProjectionBuilders or as an argument to the
// WithProjection() method for the Builder struct.
//
// Example:
//
// // projection represents the list of names {"foo", "bar", "baz", "qux"}
// oldProj := expression.NamesList(expression.Name("foo"), expression.Name("bar"))
// projection := expression.AddNames(oldProj, expression.Name("baz"), expression.Name("qux"))
//
// // Used in another Projection Expression
// anotherProjection := expression.AddNames(projection, expression.Name("quux"))
// // Used to make an Builder
// builder := expression.NewBuilder().WithProjection(newProjection)
//
// Expression Equivalent:
//
// expression.AddNames(expression.NamesList(expression.Name("foo"), expression.Name("bar")), expression.Name("baz"), expression.Name("qux"))
// "foo, bar, baz, qux"
func AddNames(projectionBuilder ProjectionBuilder, namesList ...NameBuilder) ProjectionBuilder {
projectionBuilder.names = append(projectionBuilder.names, namesList...)
return projectionBuilder
}
// AddNames returns a ProjectionBuilder representing the list of item
// attribute names equivalent to appending all of the argument item attribute
// names to the argument ProjectionBuilder. The resulting ProjectionBuilder can
// be used as a part of other ProjectionBuilders or as an argument to the
// WithProjection() method for the Builder struct.
//
// Example:
//
// // projection represents the list of names {"foo", "bar", "baz", "qux"}
// oldProj := expression.NamesList(expression.Name("foo"), expression.Name("bar"))
// projection := oldProj.AddNames(expression.Name("baz"), expression.Name("qux"))
//
// // Used in another Projection Expression
// anotherProjection := expression.AddNames(projection, expression.Name("quux"))
// // Used to make an Builder
// builder := expression.NewBuilder().WithProjection(newProjection)
//
// Expression Equivalent:
//
// expression.NamesList(expression.Name("foo"), expression.Name("bar")).AddNames(expression.Name("baz"), expression.Name("qux"))
// "foo, bar, baz, qux"
func (pb ProjectionBuilder) AddNames(namesList ...NameBuilder) ProjectionBuilder {
return AddNames(pb, namesList...)
}
// buildTree builds a tree structure of exprNodes based on the tree
// structure of the input ProjectionBuilder's child NameBuilders. buildTree()
// satisfies the treeBuilder interface so ProjectionBuilder can be a part of
// Builder and Expression struct.
func (pb ProjectionBuilder) buildTree() (exprNode, error) {
if len(pb.names) == 0 {
return exprNode{}, newUnsetParameterError("buildTree", "ProjectionBuilder")
}
childNodes, err := pb.buildChildNodes()
if err != nil {
return exprNode{}, err
}
ret := exprNode{
children: childNodes,
}
ret.fmtExpr = "$c" + strings.Repeat(", $c", len(pb.names)-1)
return ret, nil
}
// buildChildNodes creates the list of the child exprNodes.
func (pb ProjectionBuilder) buildChildNodes() ([]exprNode, error) {
childNodes := make([]exprNode, 0, len(pb.names))
for _, name := range pb.names {
operand, err := name.BuildOperand()
if err != nil {
return []exprNode{}, err
}
childNodes = append(childNodes, operand.exprNode)
}
return childNodes, nil
}
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