Question 224497 in Amazon Web Sevices Question posted in
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Amazon web services – Best way to update data in DynamoDB via a Lambda

I currently have an Express.js server hosted on a Lambda. I am already able to read/GET data from the table, with

app.get("/profile/general", async function (req, res) {
  
  const params = {
    TableName: "users",
    Key: {
      id: `${req.user.sub}`,
    },
  };

  try {
    let userObj = await docClient.get(params).promise();
    res.json({ "data": userObj });
  } catch (err) {
    console.log("error: ", err); 
    res.json({ "error": err });
  }
});

However, I am stuck researching the best/easiest way to do partial updates for items in DynamoDB (like objects in my "users" table).

I do not want to use a PUT method, because I don’t want to replace the whole existing user object. and what would the syntax look like? This is what I have so far —

app.patch("/profile/general", async function (req, res) {
  
  const params = {
    TableName: "users",
    Key: {
      id: `${req.user.sub}`,
    },
    UpdateExpression: "set age = req.body.age",
    UpdateExpression: "set country = req.body.country",
    UpdateExpression: "set skills = req.body.skills",
    ReturnValues: "ALL_NEW",
  };

  try {
    
    let newUserObj = await docClient.UpdateItem(params).promise(); 
    res.json({ "newData": newUserObj });
  } catch (err){
    console.log("error: ", err); 
    res.json({ "error": err });
  }
});

Is this the correct way to do a partial update with UpdateItem, passing in the necessary items to multiple "UpdateExpression" key-value pairs? The docs are a bit confusing on this.

Tags:

2

Answers


  1. 0

    Here is how you should update attributes for your DynamoDB record.

    const params = {
    TableName: "users",
    Key: {
      id: `${req.user.sub}`,
    },
    UpdateExpression : "SET age = :age, country = :country, skills = :skills"
    ExpressionAttributeValues: {
        ':age': req.body.age,
        ':country': req.body.country,
        ':skills': req.body.skills
    },
    ReturnValues: "ALL_NEW",
  };

    In the above code, you define the values as :<expression-attribute>, and later in ExpressionAttributeValues, you provide the actual values for those attributes.

    To learn more, refer AWS documentation at Update expressions.

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  2. 0

    It’s one UpdateExpression per update, where you specify all of the updates.

    app.patch("/profile/general", async function (req, res) {
  
  const params = {
    TableName: "users",
    Key: {
      id: `${req.user.sub}`,
    },
    UpdateExpression: `set age = ${req.body.age}, country = ${req.body.country}, skills = ${req.body.skills}`,
    ReturnValues: "ALL_NEW",
  };

  try {
    
    let newUserObj = await docClient.UpdateItem(params).promise(); 
    res.json({ "newData": newUserObj });
  } catch (err){
    console.log("error: ", err); 
    res.json({ "error": err });
  }
});
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