DynamoDB pagination example code - SST

dynamodb-pagination.ts

const LIMIT = 5
const PK = "STORE#123"

const getAuctionItems = (items: any[])=> {
  return items.map((auction)=>(getAuctionItem(auction)))
}

const getPageKey = (item: any) => ({PK:item.PK, SK:item.SK})

const encodeBase64 = (jsonItem: object)=> ( Buffer.from(JSON.stringify(jsonItem)).toString("base64")) 
const decodeBase64 = (item: string)=> ( JSON.parse(Buffer.from(item, "base64").toString())) 

export const main = handler(async (event) => {
  const LIMIT_PLUS_ONE = LIMIT + 1
  console.log(event)

  const params:  DocumentClient.QueryInput = {
    TableName: Table.Auction.tableName,
    // Limit:3,
    Limit: LIMIT_PLUS_ONE,
    KeyConditionExpression: "PK = :PK and begins_with(SK, :SKprefix)",
    // FilterExpression: `#status = :filterStatus`,
    
    ExpressionAttributeValues: {
      ":PK": PK,
      ":SKprefix": "AUC#",
      // ":filterStatus": 'active'
    },
    // ExpressionAttributeNames: {
    //   "#status":"status"
    // }

  };

  const pageAfter = event.queryStringParameters?.['pageAfter']
  const pageBefore = event.queryStringParameters?.['pageBefore']
  const filterStatus = event.queryStringParameters?.['filterStatus']

  if(pageAfter && pageBefore){
    throw new Error("Provide only one pageCursor")
  }
  const isForward = !pageBefore
  
  if(pageAfter){
    params.ExclusiveStartKey = decodeBase64(pageAfter)
  }

  if(pageBefore){
    params.ScanIndexForward = false;
    params.ExclusiveStartKey = decodeBase64(pageBefore);
  }
  let FilterExpression = ''

  if(filterStatus){
    
  }

  

  const result = await dynamoDb.query(params);

  if(!result.Items){
    return []
  }
  
  const pagination:any = {
  }
  console.log("result",result)


  const isLastOrFirstPage = result.Items.length < LIMIT_PLUS_ONE
  const slicedItems = isLastOrFirstPage ? result.Items : result.Items.slice(0,-1)

  let auctionItems;

  if(isForward){
    auctionItems = getAuctionItems(slicedItems)
    pagination.nextPageKey = isLastOrFirstPage ? undefined : encodeBase64(getPageKey(slicedItems.at(-1)))
    pagination.prevPageKey = !pageAfter && !pageBefore ? undefined : encodeBase64(getPageKey(slicedItems.at(0)))

  }else {
    const orderItems = slicedItems.reverse()
    auctionItems = getAuctionItems(orderItems)
    pagination.nextPageKey = encodeBase64(getPageKey(orderItems.at(-1)))
    pagination.prevPageKey = isLastOrFirstPage ? undefined : encodeBase64(getPageKey(orderItems.at(0)))  
  }

  return JSON.stringify({
    list:auctionItems,
    pagination
  });

  // if(isForward){
  //   const isLastPage = result.Items.length < LIMIT_PLUS_ONE
  //   const slicedItems = isLastPage ? result.Items : result.Items.slice(0,-1)
  //   const auctionItems = getAuctionItems(slicedItems)
  //   pagination.nextPageKey = isLastPage ? undefined : encodeBase64(getPageKey(slicedItems.at(-1)))
  //   pagination.prevPageKey = !pageAfterKey && !pageBeforeKey ? undefined : encodeBase64(getPageKey(slicedItems.at(0)))

  //   return JSON.stringify({
  //     list:auctionItems,
  //     pagination
  //   });
  // }else {
  //   const isFirstPage = result.Items.length < LIMIT_PLUS_ONE
  //   const slicedItems = isFirstPage ? result.Items : result.Items.slice(0,-1)
  //   const orderItems = slicedItems.reverse()
  //   const auctionItems = getAuctionItems(orderItems)
  //   pagination.nextPageKey = encodeBase64(getPageKey(orderItems.at(-1)))
  //   pagination.prevPageKey = isFirstPage ? undefined : encodeBase64(getPageKey(orderItems.at(0)))

  //   return JSON.stringify({
  //     list:auctionItems,
  //     pagination
  //   });
  // }

  
});