Having the following table definition in DynamoDB
pk: userId (string)
sk: carId (string)
index: carModelIndex (string)
If I would like to query all the cars rented by a given user for a given model. How I would go about that?.
Please note I am using the javascript sdk for dynamodb.
Related
I have set a secondary index with only a partition key (without a sort key), but I found that actually I can insert multiple items with the same partition key.
If I issue a query using the partition key in the secondary index, I'll get all the items where the partition key is equal to the given partition key value.
I'm a beginner of DynamoDB, I want to know if set a secondary index with only a partition key, but insert multiple items with the same partition key is a good idea.
I'm using Amplify.js and have this GraphQL schema:
type UserMeta #model #key(fields: ["owner"]) #auth(rules: [
{ allow: owner, operations: [create, delete, update] },
{
allow: groups,
groups: ["Admins"],
operations: [update, delete]
}
]) {
familyName: String
givenName: String
facebookUrl: AWSURL
twitterUrl: AWSURL
description: String
careers: [Career] #connection(keyName: "byOwner", fields: ["owner"])
owner: String!
}
type Career #model #key(name: "byOwner", fields: ["owner"]) #auth(rules: [
{ allow: owner, operations: [create, delete, update] },
{
allow: groups,
groups: ["Admins"],
operations: [update, delete]
}
]) {
id: ID!
company: String
companyUrl: AWSURL
industry: String
occupation: String
owner: String!
}
as you can see, the Career table has a secondary index byOwner with a partition key associated with owner(no sort key). but I can query the careers of a UserMeta normally.
with a traditional RDBMS, the index column can not be the same, I don't know why this is possible in DynamoDB, is this a best practice in DynamoDB??
Should I set a sort key for the byOwner index? maybe the sort key can be the id column?
with a traditional RDBMS, the index column can not be the same, I
don't know why this is possible in DynamoDB, is this a best practice
in DynamoDB??
Every RDBMS I've worked with allows both both unique and non-unique indexes.
The only uniqueness available in DDB is for the table's primary key.
It's very common to have records with the same partition key. In the table, records with the same partition key must have a different sort key.
For indexes, duplicates are allowed and again, this is very common use case.
One difference between RDBMS and DynamoDB is the latter expects you to know your data access patterns and use that to inform what shape the data should take. So this question ...
Should I set a sort key for the byOwner index? maybe the sort key can be the id column?
... can only be answered by knowing how you plan to load the Career objects.
If you're going to use a GraphQL query that only ever loads one at a time, like ...
type Query {
career(owner: String!, id: Id!)
}
... then adding the ID as a sort key is well worth it. It would mean the GraphQL Resolver for a Career will always be able to retrieve exactly the right object each time.
But if you'll need queries that will get a list of Career objects ...
type Query {
careers(owner: String!, since: dateString)
}
... and by default you only want to retrieve something like the "most recently created careers", then you would be better served by creating another attribute tracking when the career was created -- say createdAt: String! -- and use that as the sort key. The Resolver would then receive the list of careers by that owner in a logical sequence, allowing it to only read the oldest (or newest) careers.
This answer has some related info on how to use GSI's and sort keys with AWS AppSync.
Let's say, I have Users writing reviews of Products.
User and Product are separate entities with their own ids.
Review is an entity with a composite id composed of userId and productId.
I have created a table review in DynamoDB with both userId and productId as HASH keys.
aws dynamodb create-table --table-name review \
--attribute-definitions \
AttributeName=user_id,AttributeType=S \
AttributeName=product_id,AttributeType=S \
--key-schema \
AttributeName=user_id,KeyType=HASH \
AttributeName=product_id,KeyType=RANGE \
--provisioned-throughput ReadCapacityUnits=10,WriteCapacityUnits=5
Thus making userId+productId the composite key.
The review data object is held against that key.
Querying for a review by user and product is fine.
But how do I query for all reviews by a user or all reviews for a product?
With a single parameter, e.g. if I do a query by single key conditional expression with just "#user_id = :userId" or just "#product_id = :productId"
I get an error of the form
Query condition missed key schema element: user_id
or
Query condition missed key schema element: product_id
I have created a table review in DynamoDB with both userId and productId as HASH keys.
You've created a composite primary key for your review table, which consists of a Partition Key of userId and a and a Sort Key of 'productId' . You did not create two HASH keys.
Logically, your review table will look something like this (I've made up some data for illustration purposes):
This table structure makes it easy to fetch reviews by user. Here's an example of a query for all reviews of USER#ABC
ddbClient.query(
"TableName": "<YOUR TABLE NAME>",
"KeyConditionExpression": "#userId = :userId",
"ExpressionAttributeValues": {
":userId": {
"S": "USER#ABC"
}
},
"ExpressionAttributeNames": {
"#userId": "userId"
}
)
This will return a collection of items reviewed by USER#ABC.
DynamoDB will not allow you to fetch items by only specifying the Sort Key (e.g. productId). You always need to provide the Partition Key. So how do you get a list of Users who have reviewed a given product?
If you want to search for all Users that have reviewed a single Product, you could introduce a global secondary index that swaps the Partition Key and Sort Key of your table. This pattern is known as an inverted index. Using my example from above, an inverted index would look like this:
This would allow you to fetch users by productId:
ddbclient.query(
{
"TableName": "<YOUR TABLE NAME>",
"IndexName": "reviews_by_product_index",
"KeyConditionExpression": "#productId = :productId",
"ExpressionAttributeValues": {
":productId": {
"S": "PRODUCT#456"
}
},
"ExpressionAttributeNames": {
"#productId": "productId"
}
}
)
This query would return a collection of two items representing reviews for PRODUCT#456.
When working with a composite primary key, you can search based on conditions of the sort key as long as you also specify the partition key. That's a mouthful, but it allows you to perform queries like (in pseudocode)
query where partition key = "USER#ABC" and sort key begins_with "PRODUCT"
i have 100 records in collection,
collection name:'users'
{
"name":'senthilkumar',
"email":'senthily88#gmail.com', //HashKey
"age":21,
"created":1465733486137, //RangeKey-timestamp
}
i need to fetch records the following sql query wise
select * from users order by created desc limit 10
How i can get above query format records from DynamoDB
Dynamodb sorts the results by the range key attribute. You can set the ScanIndexForward boolean parameter to true for ascending or false for descending.
resource: http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
Use the KeyConditionExpression parameter to provide a specific value
for the partition key. The Query operation will return all of the
items from the table or index with that partition key value. You can
optionally narrow the scope of the Query operation by specifying a
sort key value and a comparison operator in KeyConditionExpression.
You can use the ScanIndexForward parameter to get results in forward
or reverse order, by sort key.
To Save Json Data to DynamoDB us put()
var Newparams = {
TableName: this.SuffleTableName,
Item: {
"userId": /* YOUR PRIMARY KEY */,
"addedAt": /* YOUR SORT KEY */,
"status": /* Additional Datas */,
}
}
Fetch Data From DynamoDB using Query()
QueryParam = {
TableName: 'YOUR TABLE NAME HERE',
IndexName: 'YOUR INDEX NAME HERE', //IF YOUR CREATED NEW INDEX
KeyConditionExpression: "UserId = :UserId ", //YOUR PRIMARY KEY
ExpressionAttributeValues: {
":UserId": UserId,
},
ScanIndexForward: false, //DESC ORDER, Set 'true' if u want asc order
ExclusiveStartKey: LastEvalVal, //Pagination - LastEvaluatedKeyPair
Limit: 10 //DataPerReq
}
If you want to return all rows in your table, you cannot use the query API, because that API requires you to provide a partition key value to filter your results by (i.e. assuming that your partition key is name you would only be able to use the query API to bring back the subset of results that have name = a given value, i.e. name= senthilkumar
If you want to return all rows in your table, you must use the Scan API: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SQLtoNoSQL.ReadData.Scan.html
Note that all results will be provided in ascending order by the value of the Range Key. You cannot reverse sort the contents with the Scan API. You would need to reverse your resultset in the application tier using whatever language you're writing your code in to turn the results upside down.
Scan does not scale well and it is not possible to use Scan to create a paginated, reverse sorted solution if your table contains items with unique partition keys.
If this is your situation, and if you want to return paginated + reverse sorted sets back from DynamoDB, you will need to re-consider the design of your table and which columns are the partition key/range key/index so that you can use the Query API.
I'm trying to model a "simple" table of 3 columns:
userId | topicId | views
The table should be able to:
have repeating userId
have repeating topicId
enforce unique combination of userId and topicId
In other words, there are many topicId's associated with a userId, and views will be a number that is incremented.
How would I create my indexes if I need to do the following queries:
get a list of records for provided userId
get and update one unique record for provided userId and topicId
Since you have more topicIds than userIds you should create your table with:
hash key - topicId
range key - userId
Add a global secondary index with:
hash key - userId
range key - topicId
You can then insert and update records using the combo topicId + userId and query for lists of topics for a specific user id.
How to query range key programmatically in DynamoDB, I am using .Net AWSSDK ,I am able to query on Hash key with below code :
GetItemRequest request = new GetItemRequest
{
TableName = tableName
};
request.Key = new Dictionary<string,AttributeValue>();
request.Key.Add("ID",new AttributeValue { S = PKValue });
GetItemResponse response = client.GetItem(request);
Please suggest,
Thanks in advance.
There are two kinds of primary key in DynamoDB: Hash-only or Hash-Range.
In the above code I guess your table is Hash-only and you use the hash key to retrieve an element with hashkey equals to PKValue.
If your table is in H-R schema and you want to retrieve a specific element with a hashKey and rangeKey, you can reuse the above code and in addition, add the {"RangeKey", new AttributeValue } into your your request.KEY
On the other hand, query means a different thing in DynamoDB. Query will return you a list of rows sorted in some order.