DynamoDB cheatsheet

Examples Use Cases

• Query
  • Get Items using begins_with on Sort Key
  • Get Items checking value in array using contains
• Put
  • Create or Update an Item
• BatchWriteItem
  • Delete a list of items

Query

Get Items using begins_with on Sort Key

Data Model

pk	sk	order	jsonObj
0	4#10#7	port	{}
0	5#2#1	x	{}
1	1#1#0	z	{}
0	4#10#9	firewall	{}
2	5#1#2	y	{}

// Query
const params = {
    TableName: "test-t",
    KeyConditionExpression: "pk = :pk AND begins_with(sk, :sk)",
    ExpressionAttributeValues: {
        ":pk": "0",
        ":sk": "4#10",
    },
};
return await db.query(params).promise();

// Output
{ Items:
   [ { sk: '4#10#7', order: 'port', pk: '0', jsonObj: [Object] },
     { sk: '4#10#9', order: 'firewall', pk: '0', jsonObj: [Object] } ],
  Count: 2,
  ScannedCount: 2 }

Get Items checking value in array using contains

Data Model

pk	sk	category
0	4#10#7	[{ "S" : "Tuna" }, { "S" : "Pizza" }, { "S" : "Ball" }]
0	5#2#1	[{ "S" : "Mouse" }, { "S" : "Hat" }]
0	1#1#0	[{ "S" : "Hat" }, { "S" : "Cheese" }]

// Query
const params = {
    TableName: "test-t",
    KeyConditionExpression: "pk = :pk",
    FilterExpression: "contains(category, :cat1) or contains(category, :cat2)",
    ExpressionAttributeValues: {
        ":pk" : "0",
        ":cat1": "Mouse",
        ":cat2": "Ball",
    }
};
return await db.query(params).promise();

// Output
{ Items:
   [ { category: [Array], pk: '0', sk: '4#10#7' },
     { category: [Array], pk: '0', sk: '5#2#1' }],
  Count: 2,
  ScannedCount: 3 }

Put

Create or Update an Item

Data Model

pk	sk	order	jsonObj
0	4#10#7	port	{}
0	5#2#1	x	{}
1	1#1#0	z	{}
0	4#10#9	firewall	{}
2	5#1#2	y	{}

// Put Operation
const params = {
    TableName: this.tableName,
    Item: {
        pk: "0"
        sk: "4#10#3",
        order: "k",
        jsonObj: {} // Can be a standard js object
    }
};
await this.db.put(params).promise();

// Output
// ...

BatchWriteItem

Delete a list of items

Limitations

• up to 16 MB of data
• 25 put or delete requests
• items to be written can be as large as 400 KB

Data Model

pk	sk	order	jsonObj
0	4#10#7	port	{}
0	5#2#1	x	{}
1	1#1#0	z	{}
0	4#10#9	firewall	{}
2	5#1#2	y	{}

// BatchWriteItem Operation
const objects = [
    {
        "pk" : "0",
        "sk" : "5#2#1",
    }, 
    {
        "pk" : "0",
        "sk" : "4#10#7",
    }
]

const params = {
    RequestItems: {} as any
};
// Add Delete Requests on this.tableName
params.RequestItems[this.tableName] = objects.map(obj => ({
    DeleteRequest: {
        Key: {
            "pk": obj.pk,
            "sk": obj.sk
        }
    }
}));
await this.db.batchWrite(params).promise();

// Output
// ...