Amazon DynamoDB DataMapper Annotations
This library provides annotations to allow easy integration of domain classes
with the DataMapper
defined in @block65/dynamodb-data-mapper
. These annotations
are provided in a separate NPM package because they rely on two experimental
features of TypeScript (decorators and metadata decoration) and depend on the
reflect-metadata
package.
Getting started
To use the annotations, you will first need to enable two TypeScript compiler
settings: experimentalDecorators
and emitDecoratorMetadata
. The former
enables the use of annotations in your project, and the latter emits type
information about declared property classes.
Next, start adding table
annotations to the domain models that represent
records in your DynamoDB tables and attribute annotations to the declared
properties that map to attributes of those records:
import {
attribute,
autoGeneratedHashKey,
rangeKey,
table,
versionAttribute,
} from '@block65/dynamodb-data-mapper-annotations';
import uuidV4 = require('uuid/v4');
@table('my_table')
class MyDomainClass {
@autoGeneratedHashKey()
id: string;
@rangeKey({defaultProvider: () => new Date()})
createdAt: Date;
@versionAttribute()
version: number;
@attribute()
toggle?: boolean;
@attribute({memberType: 'String'})
tags?: Set<string>;
// This property will not be saved to DynamoDB.
notPersistedToDynamoDb: string;
}
Using these annotations will automatically define properties at the
DynamoDbSchema
and DynamoDbTable
symbols on the class prototype, meaning
that you can pass instances of the class directly to a DataMapper
instance. No
need to define a schema separately; your class's property type declarations are
the schema.
To declare a class corresponding to a map attribute value in a DynamoDB record,
simply omit the table
annotation:
import {
attribute,
hashKey,
table,
} from '@block65/dynamodb-data-mapper-annotations';
import {embed} from '@block65/dynamodb-data-mapper';
class Comment {
@attribute()
author?: string;
@attribute()
postedAt?: Date;
@attribute()
text?: string;
}
@table('posts')
class BlogPost {
@hashKey()
id: string;
@attribute()
author?: string;
@attribute()
postedAt?: Date;
@attribute()
text?: string;
@attribute({memberType: embed(Comment)})
replies?: Array<Comment>
}
Supported Annotations
attribute
Marks a property as an attribute in the mapped DynamoDB record. The annotation will attempt to infer the correct DynamoDB type from the TypeScript type metadata, though no metadata will be available for any generic type parameters used.
attribute
must be called as a function and accepts an optional argument
containing a partial or complete field schema definition.
autoGeneratedHashKey
Designates the property as representing the record's hash key. If no key is defined, a V4 UUID will be used.
autoGeneratedHashKey
must be called as a function and accepts an optional
argument containing a partial or complete field schema definition.
hashKey
Designates the property as representing the record's hash (partition) key.
hashKey
must be called as a function and accepts an optional argument
containing a partial or complete field schema definition.
rangeKey
Designates the property as representing the record's range (sort) key.
rangeKey
must be called as a function and accepts an optional argument
containing a partial or complete field schema definition.
table
Designates a class as representing a table in DynamoDB.
table
must be called as a function with that table name as the only argument.
versionAttribute
Designates the property as representing the record's version attribute. The data
mapper will use optimistic locking by incrementing the version attribute during
put
and update
operations and sending a condition expression with all put
,
update
, and delete
operations that will cause the operation to fail if the
record in the database has a version number that does not match the one held by
the client.
versionAttribute
must be called as a function and accepts an optional argument
containing a partial or complete field schema definition.
Caveats
Reliance on experimental TypeScript features
Because this package relies on experimental TypeScript features, it is subject to change and should be considered beta software. Decorators are currently on the ECMAScript standards track, but the accepted form may differ from that implemented by TypeScript, which could cause the public interface presented by this project to change.
Lack of type information in generics
Please note that TypeScript does not emit any metadata about the type parameters
supplied to generic types, so Array<string>
, [number, string]
, and
MyClass[]
are all exposed as Array
via the emitted metadata. Without
additional metadata, this annotation will treat all encountered arrays as
collections of untyped data. You may supply either a members
declaration or a
memberType
declaration to direct this annotation to treat a property as a
tuple or typed list, respectively.
Member type declarations are required for maps and sets, though the member type
will be automatically inferred if a property is declared as being of type
BinarySet
or NumberValueSet
(from the @block65/dynamodb-auto-marshaller
package).