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thing.go
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thing.go
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package dynamodb
import (
"context"
"fmt"
"github.com/Clever/wag/samples/gen-go-db/models"
"github.com/Clever/wag/samples/gen-go-db/server/db"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/awserr"
"github.com/aws/aws-sdk-go/service/dynamodb"
"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbiface"
)
// ThingTable represents the user-configurable properties of the Thing table.
type ThingTable struct {
DynamoDBAPI dynamodbiface.DynamoDBAPI
Prefix string
ReadCapacityUnits int64
WriteCapacityUnits int64
}
// ddbThingPrimaryKey represents the primary key of a Thing in DynamoDB.
type ddbThingPrimaryKey struct {
Name string `dynamodbav:"name"`
Version int64 `dynamodbav:"version"`
}
// ddbThing represents a Thing as stored in DynamoDB.
type ddbThing struct {
ddbThingPrimaryKey
Thing models.Thing `dynamodbav:"thing"`
}
func (t ThingTable) name() string {
return fmt.Sprintf("%s-things", t.Prefix)
}
func (t ThingTable) create(ctx context.Context) error {
if _, err := t.DynamoDBAPI.CreateTableWithContext(ctx, &dynamodb.CreateTableInput{
AttributeDefinitions: []*dynamodb.AttributeDefinition{
{
AttributeName: aws.String("name"),
AttributeType: aws.String(dynamodb.ScalarAttributeTypeS),
},
{
AttributeName: aws.String("version"),
AttributeType: aws.String(dynamodb.ScalarAttributeTypeN),
},
},
KeySchema: []*dynamodb.KeySchemaElement{
{
AttributeName: aws.String("name"),
KeyType: aws.String(dynamodb.KeyTypeHash),
},
{
AttributeName: aws.String("version"),
KeyType: aws.String(dynamodb.KeyTypeRange),
},
},
ProvisionedThroughput: &dynamodb.ProvisionedThroughput{
ReadCapacityUnits: aws.Int64(t.ReadCapacityUnits),
WriteCapacityUnits: aws.Int64(t.WriteCapacityUnits),
},
TableName: aws.String(t.name()),
}); err != nil {
return err
}
return nil
}
func (t ThingTable) saveThing(ctx context.Context, m models.Thing) error {
data, err := encodeThing(m)
if err != nil {
return err
}
_, err = t.DynamoDBAPI.PutItemWithContext(ctx, &dynamodb.PutItemInput{
TableName: aws.String(t.name()),
Item: data,
ExpressionAttributeNames: map[string]*string{
"#NAME": aws.String("name"),
"#VERSION": aws.String("version"),
},
ConditionExpression: aws.String("attribute_not_exists(#NAME) AND attribute_not_exists(#VERSION)"),
})
if err != nil {
if awsErr, ok := err.(awserr.Error); ok {
if awsErr.Code() == dynamodb.ErrCodeConditionalCheckFailedException {
return db.ErrThingAlreadyExists{
Name: m.Name,
Version: m.Version,
}
}
}
return err
}
return nil
}
func (t ThingTable) getThing(ctx context.Context, name string, version int64) (*models.Thing, error) {
key, err := dynamodbattribute.MarshalMap(ddbThingPrimaryKey{
Name: name,
Version: version,
})
if err != nil {
return nil, err
}
res, err := t.DynamoDBAPI.GetItemWithContext(ctx, &dynamodb.GetItemInput{
Key: key,
TableName: aws.String(t.name()),
})
if err != nil {
return nil, err
}
if len(res.Item) == 0 {
return nil, db.ErrThingNotFound{
Name: name,
Version: version,
}
}
var m models.Thing
if err := decodeThing(res.Item, &m); err != nil {
return nil, err
}
return &m, nil
}
func (t ThingTable) deleteThing(ctx context.Context, name string, version int64) error {
key, err := dynamodbattribute.MarshalMap(ddbThingPrimaryKey{
Name: name,
Version: version,
})
if err != nil {
return err
}
_, err = t.DynamoDBAPI.DeleteItemWithContext(ctx, &dynamodb.DeleteItemInput{
Key: key,
TableName: aws.String(t.name()),
})
if err != nil {
return err
}
return nil
}
// encodeThing encodes a Thing as a DynamoDB map of attribute values.
func encodeThing(m models.Thing) (map[string]*dynamodb.AttributeValue, error) {
return dynamodbattribute.MarshalMap(ddbThing{
ddbThingPrimaryKey: ddbThingPrimaryKey{
Name: m.Name,
Version: m.Version,
},
Thing: m,
})
}
// decodeThing translates a Thing stored in DynamoDB to a Thing struct.
func decodeThing(m map[string]*dynamodb.AttributeValue, out *models.Thing) error {
var ddbThing ddbThing
if err := dynamodbattribute.UnmarshalMap(m, &ddbThing); err != nil {
return err
}
*out = ddbThing.Thing
return nil
}