I have a DynamoDB table that I need to read/write to. I am trying to create a model for reading and writing from DynamoDB with Kotlin. But I keep encountering com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: MyModelDB[myMap]; could not unconvert attribute when I run dynamoDBMapper.scanPage(...). Some times myMap will be MyListOfMaps instead, but I guess it's from iterating the keys of a Map.
My code is below:
#DynamoDBTable(tableName = "") // Non-issue, I am assigning the table name in the DynamoDBMapper
data class MyModelDB(
#DynamoDBHashKey(attributeName = "id")
var id: String,
#DynamoDBAttribute(attributeName = "myMap")
var myMap: MyMap,
#DynamoDBAttribute(attributeName = "MyListOfMapItems")
var myListOfMapItems: List<MyMapItem>,
) {
constructor() : this(id = "", myMap = MyMap(), myListOfMaps = mutableListOf())
#DynamoDBDocument
class MyMap {
#get:DynamoDBAttribute(attributeName = "myMapAttr")
var myMapAttr: MyMapAttr = MyMapAttr()
#DynamoDBDocument
class MyMapAttr {
#get:DynamoDBAttribute(attributeName = "stringValue")
var stringValue: String = ""
}
}
#DynamoDBDocument
class MyMapItem {
#get:DynamoDBAttribute(attributeName = "myMapItemAttr")
var myMapItemAttr: String = ""
}
}
I am using the com.amazonaws:aws-java-sdk-dynamodb:1.11.500 package and my dynamoDBMapper is initialised with DynamoDBMapperConfig.Builder().build() (along with some other configurations).
My question is what am I doing wrong and why? I have also seen that some Java implementations use DynamoDBTypeConverter. Is it better and I should be using that instead?
Any examples would be appreciated!
A couple comments here. First, you are not using the AWS SDK for Kotlin. You are using another SDK and simply writing Kotlin code. Using this SDK, you are not getting full benefits of Kotlin such as support of Coroutines.
The AWS SDK for Kotlin (which does offer full support of Kotlin features) was just released as DEV Preview this week. See the DEV Guide:
Setting up the AWS SDK for Kotlin
However this SDK does not support this mapping as of now. To place items into an Amazon DynamoDB table using the AWS SDK for Kotlin, you need to use:
mutableMapOf<String, AttributeValue>
Full example here.
To map Java Objects to a DynamoDB table, you should look at using the DynamoDbEnhancedClient that is part of AWS SDK for Java V2. See this topic in the AWS SDK for Java V2 Developer Guide:
Mapping items in DynamoDB tables
You can find other example of using the Enhanced Client in the AWS Github repo.
Ok, I eventually got this working thanks to some help. I edited the question slightly after getting a better understanding. Here is how my data class eventually turned out. For Java users, Kotlin compiles to Java, so if you can figure out how the conversion works, the idea should be the same for your use too.
data class MyModelDB(
#DynamoDBHashKey(attributeName = "id")
var id: String = "",
#DynamoDBAttribute(attributeName = "myMap")
#DynamoDBTypeConverted(converter = MapConverter::class)
var myMap: Map<String, AttributeValue> = mutableMapOf(),
#DynamoDBAttribute(attributeName = "myList")
#DynamoDBTypeConverted(converter = ListConverter::class)
var myList: List<AttributeItem> = mutableListOf(),
) {
constructor() : this(id = "", myMap = MyMap(), myList = mutableListOf())
}
class MapConverter : DynamoDBTypeConverter<AttributeValue, Map<String,AttributeValue>> {
override fun convert(map: Map<String,AttributeValue>>): AttributeValue {
return AttributeValue().withM(map)
}
override fun unconvert(itemMap: AttributeValue?): Map<String,AttributeValue>>? {
return itemMap?.m
}
}
class ListConverter : DynamoDBTypeConverter<AttributeValue, List<AttributeValue>> {
override fun convert(list: List<AttributeValue>): AttributeValue {
return AttributeValue().withL(list)
}
override fun unconvert(itemList: AttributeValue?): List<AttributeValue>? {
return itemList?.l
}
}
This would at least let me use my custom converters to get my data out of DynamoDB. I would go on to define a separate data container class for use within my own application, and I created a method to serialize and unserialize between these 2 data objects. This is more of a preference for how you would like to handle the data, but this is it for me.
// For reading and writing to DynamoDB
class MyModelDB {
...
fun toMyModel(): MyModel {
...
}
}
// For use in my application
class MyModel {
var id: String = ""
var myMap: CustomObject = CustomObject()
var myList<CustomObject2> = mutableListOf()
fun toMyModelDB():MyModelDB {
...
}
}
Finally, we come to the implementation of the 2 toMyModel.*() methods. Let's start with input, this is what my columns looked like:
myMap:
{
"key1": {
"M": {
"subKey1": {
"S": "some"
},
"subKey2": {
"S": "string"
}
}
},
"key2": {
"M": {
"subKey1": {
"S": "other"
},
"subKey2": {
"S": "string"
}
}
}
}
myList:
[
{
"M": {
"key1": {
"S": "some"
},
"key2": {
"S": "string"
}
}
},
{
"M": {
"key1": {
"S": "some string"
},
"key3": {
"M": {
"key4": {
"S": "some string"
}
}
}
}
}
]
The trick then is to use com.amazonaws.services.dynamodbv2.model.AttributeValue to convert each field in the JSON. So if I wanted to access the value of subKey2 in key1 field of myMap, I would do something like this:
myModelDB.myMap["key1"]
?.m // Null check and get the value of key1, a map
?.get("subKey2") // Get the AttributeValue associated with the "subKey2" key
?.s // Get the value of "subKey2" as a String
The same applies to myList:
myModelDB.myList.foreach {
it?.m // Null check and get the map at the current index
?.get("key1") // Get the AttributeValue associated with the "key1"
...
}
Edit: Doubt this will be much of an issue, but I also updated my DynamoDB dependency to com.amazonaws:aws-java-sdk-dynamodb:1.12.126
I have an AppSync API that I'm using for an app. One action I'm trying to do is have a Lambda function that collects certain data fire off a GraphQL mutation, and then have a subscription on my front end collect that data when the mutation is called. This data is ephemeral and I don't want to write it to a database, so I'm trying to set up a "None" data source in AppSync just to pass this data off.
I have an AppSync GraphQL API set up with the following (simplified) schema:
type Mutation #aws_api_key
#aws_cognito_user_pools {
sendSearchResults(input: SearchResultInputHeader!): SearchResultOutputHeader
}
input SearchResultInput {
assetId: String
score: Float
}
input SearchResultInputHeader {
callId: String
results: [SearchResultInput]
}
type SearchResultOutput #aws_api_key
#aws_cognito_user_pools {
assetId: String
score: Float
}
type SearchResultOutputHeader #aws_api_key
#aws_cognito_user_pools {
callId: String
results: [SearchResultOutput]
}
and the following request / response resolver mappings:
// REQUEST::
{
"version": "2017-02-28",
"payload": {
"callId": "${context.arguments.input.callId}",
"results": "${context.arguments.input.results}"
}
}
// RESPONSE::
$util.toJson($context.result)
I am able to pass the callId String through this mutation but I am unable to get the results to pass through
// INPUT::
mutation MyMutation {
sendSearchResults(input: {resultsIn: [{assetId: "0001", score: 10}, {assetId: "0002", score: 22}], callId: "aaa-aaa-aaa"}) {
callId
resultsOut {
assetId
}
}
}
// RETURN::
{
"data": {
"sendSearchResults": {
"callId": "aaa-aaa-aaa",
"resultsOut": null
}
}
}
So I have two main questions:
How can I get the resolver/mutation to return a list of results rather than null?
Any other suggestions on passing data through an AppSync mutation and subscription? Or does this approach seem to make sense without writing to a database and just receiving a key?
Thanks!
// REQUEST::
{
"version": "2017-02-28",
"payload": {
"callId": "${context.arguments.input.callId}",
"results": "${context.arguments.input.results}"
}
}
// INPUT::
mutation MyMutation {
sendSearchResults(input: {resultsIn: [{assetId: "0001", score: 10}, {assetId: "0002", score: 22}], callId: "aaa-aaa-aaa"}) {
callId
resultsOut {
assetId
}
}
}
Here is results and resultsIn are different is two places.
Working with apollo is great but how can you change the shape of the response from a query. I am using reactjs to display user details and their music information
Say I have a query
query {
userDetails {
id,
name,
music {
name,
type
}
}
is there a way to change the shape using apollo (not in reactjs) to something like
query {
userDetails {
id,
name,
musicName,
musicType
}
}
so that I get the second shape as the response rather than the first, then which I will have to change it using reactjs
You can create local-only fields that reads from the fetched fields by using the #client-directive and TypePolicies
Assuming the typename returned from the query is "User":
Query:
query {
userDetails {
id,
name,
music {
name,
type
}
musicName#client
musicType#client
}
Client setup:
const client = new ApolloClient({
cache: new InMemoryCache({
typePolicies: {
User: {
fields: {
musicName: {
read(_, { readField }) {
return readField('music').name;
}
},
musicType: {
read(_, { readField }) {
return readField('music').type;
}
},
}
}
}
}),
uri: "yourGraphqlServer.com"
});
I created this question in case anyone was curious on how to add union / Polymorphic types in Apollo. Hopefully this will make it easier for them.
In this example I wanted the response to either be a Worksheet or ApiError
// typedefs.js
export default [`
schema {
query: Query
}
type Query {
worksheet(id: String!): Worksheet | Error
}
type Worksheet {
id: String!
name String
}
type ApiError {
code: String!
message: String!
}
`];
// resolvers.js
export default {
Query: {
worksheet(_, args, { loaders }) {
return loaders.worksheet.get(args.id).catch(() => {
// ApiError
return {
code: '1',
message: 'test'
}
});
}
}
};
// Express Server
import { graphqlExpress } from 'apollo-server-express';
import { makeExecutableSchema } from 'graphql-tools';
import typeDefs from './typedefs';
import resolvers from './resolvers';
...
app.post(
'/graphql',
graphqlExpress(req => ({
makeExecutableSchema({ typeDefs, resolvers }),
context: mkRequestContext(req.ctx, req.log),
formatError: formatGraphQLError(req.ctx, req.log)
}))
);
In GraphQL to add a union type in the typedefs you have to define the union
i.e union WorksheetOrError = Worksheet | ApiError
// typedefs.js
export default [
`
schema {
query: Query
}
type Query {
worksheet(id: String!): WorksheetOrError
}
union WorksheetOrError = Worksheet | ApiError
type Worksheet {
id: String!
name String
}
type ApiError {
code: String!
message: String!
}
`];
In the resolvers you have to define a resolver for the union type that has the property __resolveType. This will help tell the GraphQL executor which type the result is.
// resolvers.js
export default {
Query: {
worksheet() {
...
}
},
WorksheetOrError: {
__resolveType(obj) {
if (obj.id) {
return 'Worksheet';
}
if (obj.code) {
return 'ApiError';
}
return null;
}
},
};
To create a GraphQL Query in Apollo Client
// Your application code.
// This is my Worksheet Query in my React code.
const WorksheetQuery = gql`
query GetWorksheet($worksheetId: String!) {
worksheet(id: $worksheetId) {
... on Worksheet {
id
name
}
... on ApiError {
code
message
}
}
}
Now you can check the __typename to check what type is in the response.
Note: For those who are wondering why I'm not using GraphQL errors. It's because Apollo doesn't seem to handle errors well when it encounters a graphQL error. So for a work around I'm trying to return a custom ApiError in my response.
There a few reasons why using a union with an error type is nice.
Currently if you wanted a partial response with GraphQLError. Apollo does not cache the errors so if you wanted to re-use the cached response later you wouldn't have the complete response since the errors are removed. (Now you can't display the proper UI with errors)
Getting GraphQLError back in Apollo would return a flat list of errors with the path to where the error is in the data. So you would need to verify that which part of your schema did the error occur in. However if you follow the instructions above you would have the error within the schema already. That way you already know which part of the schema the error happened.
In MongoDB, is it possible to update the value of a field using the value from another field? The equivalent SQL would be something like:
UPDATE Person SET Name = FirstName + ' ' + LastName
And the MongoDB pseudo-code would be:
db.person.update( {}, { $set : { name : firstName + ' ' + lastName } );
The best way to do this is in version 4.2+ which allows using the aggregation pipeline in the update document and the updateOne, updateMany, or update(deprecated in most if not all languages drivers) collection methods.
MongoDB 4.2+
Version 4.2 also introduced the $set pipeline stage operator, which is an alias for $addFields. I will use $set here as it maps with what we are trying to achieve.
db.collection.<update method>(
{},
[
{"$set": {"name": { "$concat": ["$firstName", " ", "$lastName"]}}}
]
)
Note that square brackets in the second argument to the method specify an aggregation pipeline instead of a plain update document because using a simple document will not work correctly.
MongoDB 3.4+
In 3.4+, you can use $addFields and the $out aggregation pipeline operators.
db.collection.aggregate(
[
{ "$addFields": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}},
{ "$out": <output collection name> }
]
)
Note that this does not update your collection but instead replaces the existing collection or creates a new one. Also, for update operations that require "typecasting", you will need client-side processing, and depending on the operation, you may need to use the find() method instead of the .aggreate() method.
MongoDB 3.2 and 3.0
The way we do this is by $projecting our documents and using the $concat string aggregation operator to return the concatenated string.
You then iterate the cursor and use the $set update operator to add the new field to your documents using bulk operations for maximum efficiency.
Aggregation query:
var cursor = db.collection.aggregate([
{ "$project": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}}
])
MongoDB 3.2 or newer
You need to use the bulkWrite method.
var requests = [];
cursor.forEach(document => {
requests.push( {
'updateOne': {
'filter': { '_id': document._id },
'update': { '$set': { 'name': document.name } }
}
});
if (requests.length === 500) {
//Execute per 500 operations and re-init
db.collection.bulkWrite(requests);
requests = [];
}
});
if(requests.length > 0) {
db.collection.bulkWrite(requests);
}
MongoDB 2.6 and 3.0
From this version, you need to use the now deprecated Bulk API and its associated methods.
var bulk = db.collection.initializeUnorderedBulkOp();
var count = 0;
cursor.snapshot().forEach(function(document) {
bulk.find({ '_id': document._id }).updateOne( {
'$set': { 'name': document.name }
});
count++;
if(count%500 === 0) {
// Excecute per 500 operations and re-init
bulk.execute();
bulk = db.collection.initializeUnorderedBulkOp();
}
})
// clean up queues
if(count > 0) {
bulk.execute();
}
MongoDB 2.4
cursor["result"].forEach(function(document) {
db.collection.update(
{ "_id": document._id },
{ "$set": { "name": document.name } }
);
})
You should iterate through. For your specific case:
db.person.find().snapshot().forEach(
function (elem) {
db.person.update(
{
_id: elem._id
},
{
$set: {
name: elem.firstname + ' ' + elem.lastname
}
}
);
}
);
Apparently there is a way to do this efficiently since MongoDB 3.4, see styvane's answer.
Obsolete answer below
You cannot refer to the document itself in an update (yet). You'll need to iterate through the documents and update each document using a function. See this answer for an example, or this one for server-side eval().
For a database with high activity, you may run into issues where your updates affect actively changing records and for this reason I recommend using snapshot()
db.person.find().snapshot().forEach( function (hombre) {
hombre.name = hombre.firstName + ' ' + hombre.lastName;
db.person.save(hombre);
});
http://docs.mongodb.org/manual/reference/method/cursor.snapshot/
Starting Mongo 4.2, db.collection.update() can accept an aggregation pipeline, finally allowing the update/creation of a field based on another field:
// { firstName: "Hello", lastName: "World" }
db.collection.updateMany(
{},
[{ $set: { name: { $concat: [ "$firstName", " ", "$lastName" ] } } }]
)
// { "firstName" : "Hello", "lastName" : "World", "name" : "Hello World" }
The first part {} is the match query, filtering which documents to update (in our case all documents).
The second part [{ $set: { name: { ... } }] is the update aggregation pipeline (note the squared brackets signifying the use of an aggregation pipeline). $set is a new aggregation operator and an alias of $addFields.
Regarding this answer, the snapshot function is deprecated in version 3.6, according to this update. So, on version 3.6 and above, it is possible to perform the operation this way:
db.person.find().forEach(
function (elem) {
db.person.update(
{
_id: elem._id
},
{
$set: {
name: elem.firstname + ' ' + elem.lastname
}
}
);
}
);
I tried the above solution but I found it unsuitable for large amounts of data. I then discovered the stream feature:
MongoClient.connect("...", function(err, db){
var c = db.collection('yourCollection');
var s = c.find({/* your query */}).stream();
s.on('data', function(doc){
c.update({_id: doc._id}, {$set: {name : doc.firstName + ' ' + doc.lastName}}, function(err, result) { /* result == true? */} }
});
s.on('end', function(){
// stream can end before all your updates do if you have a lot
})
})
update() method takes aggregation pipeline as parameter like
db.collection_name.update(
{
// Query
},
[
// Aggregation pipeline
{ "$set": { "id": "$_id" } }
],
{
// Options
"multi": true // false when a single doc has to be updated
}
)
The field can be set or unset with existing values using the aggregation pipeline.
Note: use $ with field name to specify the field which has to be read.
Here's what we came up with for copying one field to another for ~150_000 records. It took about 6 minutes, but is still significantly less resource intensive than it would have been to instantiate and iterate over the same number of ruby objects.
js_query = %({
$or : [
{
'settings.mobile_notifications' : { $exists : false },
'settings.mobile_admin_notifications' : { $exists : false }
}
]
})
js_for_each = %(function(user) {
if (!user.settings.hasOwnProperty('mobile_notifications')) {
user.settings.mobile_notifications = user.settings.email_notifications;
}
if (!user.settings.hasOwnProperty('mobile_admin_notifications')) {
user.settings.mobile_admin_notifications = user.settings.email_admin_notifications;
}
db.users.save(user);
})
js = "db.users.find(#{js_query}).forEach(#{js_for_each});"
Mongoid::Sessions.default.command('$eval' => js)
With MongoDB version 4.2+, updates are more flexible as it allows the use of aggregation pipeline in its update, updateOne and updateMany. You can now transform your documents using the aggregation operators then update without the need to explicity state the $set command (instead we use $replaceRoot: {newRoot: "$$ROOT"})
Here we use the aggregate query to extract the timestamp from MongoDB's ObjectID "_id" field and update the documents (I am not an expert in SQL but I think SQL does not provide any auto generated ObjectID that has timestamp to it, you would have to automatically create that date)
var collection = "person"
agg_query = [
{
"$addFields" : {
"_last_updated" : {
"$toDate" : "$_id"
}
}
},
{
$replaceRoot: {
newRoot: "$$ROOT"
}
}
]
db.getCollection(collection).updateMany({}, agg_query, {upsert: true})
(I would have posted this as a comment, but couldn't)
For anyone who lands here trying to update one field using another in the document with the c# driver...
I could not figure out how to use any of the UpdateXXX methods and their associated overloads since they take an UpdateDefinition as an argument.
// we want to set Prop1 to Prop2
class Foo { public string Prop1 { get; set; } public string Prop2 { get; set;} }
void Test()
{
var update = new UpdateDefinitionBuilder<Foo>();
update.Set(x => x.Prop1, <new value; no way to get a hold of the object that I can find>)
}
As a workaround, I found that you can use the RunCommand method on an IMongoDatabase (https://docs.mongodb.com/manual/reference/command/update/#dbcmd.update).
var command = new BsonDocument
{
{ "update", "CollectionToUpdate" },
{ "updates", new BsonArray
{
new BsonDocument
{
// Any filter; here the check is if Prop1 does not exist
{ "q", new BsonDocument{ ["Prop1"] = new BsonDocument("$exists", false) }},
// set it to the value of Prop2
{ "u", new BsonArray { new BsonDocument { ["$set"] = new BsonDocument("Prop1", "$Prop2") }}},
{ "multi", true }
}
}
}
};
database.RunCommand<BsonDocument>(command);
MongoDB 4.2+ Golang
result, err := collection.UpdateMany(ctx, bson.M{},
mongo.Pipeline{
bson.D{{"$set",
bson.M{"name": bson.M{"$concat": []string{"$lastName", " ", "$firstName"}}}
}},
)