Dynamodb Node js (Dynamoose) 中的一对多关系

Question

I am using Dynamodb with nodejs for my reservation system. And Dynamoose as ORM. I have two tables ie Table and Reservation . To create relation between them, I have added tableId attribute in Reservation which is of type Model type (of type Table type), as mentioned in the dyanmoose docs . Using the document.populate I am able to get the Table data through the tableId attribute from Reservation table. But how can I retrieve all Reservation for a Table ? (Reservation and Table has one to many relation)?

These are my Model: Table Model:

    const tableSchema = new Schema ({
        tableId: {
            type: String,
            required: true,
            unique: true,
            hashKey: true
        },
        name: {
             type: String,
             default: null
        },
    });

*Reservation Model:*

    const reservationSchema = new Schema ({
        id: {
            type: Number,
            required: true,
            unique: true,
            hashKey: true
        },
        tableId: table,   \\as per doc attribute of Table (Model) type 
        date: {
            type: String
        }
    });

This is how I retrieve table data from reservation model

reservationModel.scan().exec()
        .then(posts => {
            return posts.populate({
                path: 'tableId',
                model: 'Space'
              });
        })
        .then(populatedPosts => {
        
            console.log('pp',populatedPosts);
            return {
                allData: {
                  message: "Executedddd succesfully",
                  data: populatedPosts
                }
              }
        })

Anyone please help to retrieve all Reservation data from Table??

Answer 1

As of v2.8.2, Dynamoose does not support this. Dynamoose is focused on one directional simple relationships. This is partly due to the fact that we discourage use of model.populate . It is important to note that model.populate does another completely separate request to DynamoDB. This increases the latency and decreases the performance of your application.

DynamoDB truly requires a shift in how you think about modeling your data compared to SQL. I recommend watching AWS re:Invent 2019: Data modeling with Amazon DynamoDB (CMY304) for a great explanation of how you can model your data in DynamoDB in a highly efficient manner.

At some point Dynamoose might add support for this, but it's really hard to say if we will.

If you truly want to do this, I'd recommend adding a global index to your tableId property in your reservation schema. Then you can run something like the following:

async function code(id) {
    const reservation = await reservationModel.get(id);
    const tables = await tableModel.query("tableId").eq(id).exec(); // This will be an array of `table` entries where `"tableId"=id`. Remember, it is required you add an index for this to work.
}

Remember, this will cause multiple calls to DynamoDB and isn't as efficient. I'd highly recommend watching the video I linked above to get more information about how to model your data in an more efficient manner.

Finally, I'd like to point out that your unique: true code does nothing. As seen in the Dynamoose Attribute Settings Documentation , unique is not a valid setting. In your case since you don't have a rangeKey , it's not possible for two items to have the same hashKey , so technically it's already a unique property based on that. However it is important to note that you can overwrite existing items when creating an item. You can set overwrite to false for document.save or Model.create to prevent that behavior and throw an error instead of overwriting your document.