I have an existing table which has 10 fields. Fields are like this:
AuthID, UserID, Age, Job, .etc
The table stores data of my users. "AuthID" is primary key and "UserID" is a Global Secondary Index.
When I get item by AuthID, everything is fine. But I can't get item by UserID. I tried GetItem, Query and Scan methods but I failed in all three method.
I need to be able to get data with these 3 methods I wrote below :
1 - Get user data by AuthID (It's already works fine)
2 - Get user data by UserID
3 - Get user data by AuthID and UserID both
AuthID and UserID is unique. Can someone point me right way as to what to do?
I have searched a lot in the documentation and found that if you need to get a single item even then you cant use the get or getItem method when using a global secondary index. One can use the query method. a sample of query method with global secondary index is
let params = {
TableName: "Users",
IndexName: "your-index",
ExpressionAttributeValues: {
":v1": "myid"
},
KeyConditionExpression: "my_partition_key_in_gsi = :v1",
};
dynamodb.query(params, function(err, data) {
if (err) console.log(err, err.stack); // an error occurred
else console.log(data); // successful response
});
Related
I'm using DynamoDB for my new Serverless Restful API with nodejs.
The Restful API supports query for resources with the limit and lastKey query parameters for key pagination.
Assume there's a table like below:
PK
SK
School
firstSchool
School
secondSchool
School
thirdSchool
PK is partition key, and SK is sort key.
I use SK for key pagination.
If I call the api with http://somewhere/api/school?limit=1&lastKey=secondSchool, ExclusiveStartKey in query will be {"PK" : "School", "SK" : "secondSchool"}, and the returned item will be {"PK" : "School", "SK" : "thirdSchool"}.
It works well in that case, but the problem is the same result is created with the url like http://somewhere/api/school?limit=1&lastKey=seco.
In this case, ExclusiveStartKey in query will be {"PK" : "School", "SK" : "seco"}
It seems DynamoDB doesn't use exact match for a sk value in ExclusiveStartKey.
Is there any way to force DynamoDB to use exact match for ExclusiveStartKey?
I attach my test code below:
const { DynamoDBClient } = require("#aws-sdk/client-dynamodb");
const { DynamoDBDocument } = require("#aws-sdk/lib-dynamodb");
const ddbClient = new DynamoDBClient({
region: AWS_REGION,
endpoint: AWS_DYNAMODB_END_POINT,
credentials: {
accessKeyId: AWS_ACCESSKEY_ID,
secretAccessKey: AWS_SECRET_ACCESS_KEY,
},
});
const ddbDocClient = DynamoDBDocument.from(ddbClient);
(async () => {
try {
const data = await ddbDocClient.query({
TableName: "Table Name",
KeyConditionExpression: "#pk = :pk",
ExpressionAttributeNames: {
"#pk": "PK",
},
ExpressionAttributeValues: {
":pk": "Test",
},
Limit: 1,
ExclusiveStartKey: { PK: "Test", SK: "Seco" },
});
console.log(data);
} catch (err) {
console.log("Error", err);
}
})();
The ExclusiveKeyStart is used mainly for paging large Scan or Query requests - i.e., retrieving the next page of results after the previous page ended with a LastEvaluatedKey, and you are supposed to give exactly that key (not some subset of it...) as the ExclusiveKeyStart of the next request.
You are trying to do something different, and to achieve you can't use ExclusiveKeyStart, but you can use something else:
The Query request has a KeyConditionExpression. You can specify sk > :value as a key condition expression (don't pass ExclusiveKeyStart), and you'll get this all the sort keys higher than that :value like your string "seco". Please note, however, that because your sort key is truncated, this result may actually include one or more extra results before the first key you want (e.g., the keys "seco" and "secoaaaa" come before "secondSchool") so you may need to drop them yourself from the results.
The KeyConditionExpression is implemented efficiently - DynamoDB knows how to skip directly to that sort key in the partition, and doesn't charge you for reading the entire partition, so in this respect it is just as good as ExclusiveKeyStart.
It is possible to somehow filter results by key name that stored in the same object?
I have JSON object "keys", in property "default" stored key of the object that I need. Is it somehow possible to filter like that keys[keys.default].type = some_type?
var params = {
TableName: 'TABLE_NAME',
IndexName: 'TABLE_INDEX', // optional (if querying an index)
KeyConditionExpression: 'myId = :value',
FilterExpression: '#kmap[#kmap.#def].#tp = :keyval',
ExpressionAttributeNames: {names with special characters
'#kmap': 'keys',
'#tp': 'type',
'#def': 'default'
},
ExpressionAttributeValues: { // a map of substitutions for all attribute values
':value': '1',
':keyval': 'some_type'
},
Limit: 10, // optional (limit the number of items to evaluate)
ProjectionExpression: "displayName, #kmap",
ReturnConsumedCapacity: 'TOTLAL', // optional (NONE | TOTAL | INDEXES)
};
docClient.query(params, function(err, data) {
if (err) ppJson(err); // an error occurred
else ppJson(data); // successful response
});
I'm pretty sure the answer is no.
This keys[keys.default] is not even valid json, as far as I can tell.
Of course, you can do this in two steps:
First, query to get the default key
Then query to get the value
Don't forget, filters are obly applied to the result set - it still requires a libear traversal as specified by your Query or Scan operation.
So you can probably more easily run your query on the client.
And lastly, if this is a typical query ypu need to perform, as an optimization, you can lift the default key and value to be top level attributes on the item. Thrn you can actually create a GSI on that attribure and can actually do efficient lookups.
I am trying to access to a object into another object in my firebase database, i have a structure like this:
I want to get all the objects that have the email that i send by parameters, i am using .child to access to the childs into my object but i am not success with the query, this is my code
$ ref_db.child("/groups").child("members").orderByChild("email").equalTo(email).once("value", (snapshot)=>{
console.log(snapshot.val());
});
The snapshot.val() always is undefined.
could you help me with the query?
One efficient way to get "all the groups that have that email inside the members object" would be to denormalize you data and have another "main node" in your database where you store all "members" (i.e. their email) and the "groups" they belong to.
This means that each time you add a "member" node under a "group" (including its email) you will also add the group as a child of the member email, in this other "main node".
More concretely, here is how would be the database structure:
Your current structure:
- groups
- -LB9o....
...
- members
- -LB9qbd....
-email: xxxx#zzz.com
- -LBA7R....
-email: yyyyy#aaaa.com
And the extra structure:
- groupsByMembers
- xxxxxx#zzzcom
- Grupo1: true
- yyyyy#aaaacom
- Grupo1: true
- Grupo2: true
- bbbcccc#dddcom
- Grupo6: true
- Grupo8: true
Note that in the "extra structure" the dots within an email address are removed, since you cannot include a point in a node id. You will have to remove them accordingly when writing and querying.
This way you can easily query for the list of groups a member is belonging to, as shown below. Without the need to loop several times over several items. This dernomalization technique is quite classic in NoSQL databases.
const mailToSearchFor = xxxx.xx#zzz.com;
const ref = database.ref('/groupsByMembers/' + mailToSearchFor.replace(/\./g, ''));
ref.once('value', snapshot => {
const val = snapshot.val();
for (let key in val) {
if (val.hasOwnProperty(key)) {
console.log(key);
}
}
});
In order to write to the two database nodes simultaneously, use the update method as explained here https://firebase.google.com/docs/database/web/read-and-write#update_specific_fields
This is because you have a random key before members, you need to go through the path and not skip a node, to be able to access the values:
ref_db.child("groups").child("-LB9oWcnE0wXx8PbH4D").child("members").orderByChild("email").equalTo(email).once("value", (snapshot)=>{
console.log(snapshot.val());
});
I want to retrieve data of current user in the application. How can I do that. ?
Here is my current user's firebase id :
And my table node is :
Here it is clear that my uid and nodes title are different. So how can I get particular user's data.
My code till now:
self.ref = Database.database().reference()
let userID = Auth.auth().currentUser?.uid
self.ref.child("member").child(userID!).observeSingleEvent(of: .value, with: { (snapshot) in
if !snapshot.exists() {
// handle data not found
return
}
})
You are getting different IDs, because the first one Wnlxl... is the userID and the other -KVvR664... is an autoID.
You have set .childByAutoID following the member, if you want to retrieve the data of the current user then, you have to put userID following member.
Then you can easily retrieve the user's data by userID because each and every detail will be saved under userID.
Hope this code will work for you.
let ref : FIRDatabaseReference!
ref = FIRDatabase.database().reference()
ref.child("member").child(user!.uid).setValue(["name": self.fullName.text!, "email": self.email.text!, "mobile": self.mobile.text!, "doj": self.doj.text!])
Your Firebase screenshot is incorrect I think - your code will work fine, but how you create these members are wrong.
When creating the members you are saying .childByAutoID which you should be using Auth.auth().currentUser?.uid. If that makes sense. Let me know.
Edit: to create a user with userUID data in the node member do the following:
if let userUID = Auth().auth.currentUser?.uid{
ref.child("members/\(userUID)").setValue(*YOURMEMBERINFODICTIONARY*)
}
I have a pre-existing data in the form of JSON files which I am trying to insert into Sequelize SQLite table. I have 2 tables: Master_Vessel and Requests. There is a Request.hasOne(Vessel) association, meaning that every request has a vessel associated with it.
The key connecting both the models is vessel.Vessel_Name, which is a string. The data has been generated from a system which validates the keys so it is consistent (every request.Vessel_Name exists in vessel.Vessel_Name, vessel.Vessel_Name is unique).
I want to load this data into Sequelize managed table. I am creating the models as follows:
var Request = sequelize.define('request', {
// other fields
Vessel_Name: {
type: Sequelize.STRING
}
}, {
tableName: 'Request'
});
var Vessel = sequelize.define('vessel', {
// other fields
Vessel_Name: {
type: Sequelize.STRING,
primaryKey: true
}
}, {
tableName: 'Master_Vessel'
});
And, the association is as follows:
Request.hasOne(Vessel, {foreignKey: 'Vessel_Name', allowNull: true});
Now, I am loading the data in following steps:
Create and bulk load the Vessel model
Create the Request model, the association and bulk load the Request model
Everything runs fine without any issues. However when I try to query using the association as follows:
Request.findOne()
.then(request => {
console.log(request.get())
request.getVessel()
.then(vessel => console.log(vessel))
});
request instance contains the Vessel_Name foreign key, however the vessel instance is null.
Can anybody please help?
Okay this is happenning because I got the Sequelize 'vocabulary' mixed up, Request.hasOne(Vessel) does NOT mean Request will have one Vessel_Name that will point to a Vessel. It is to be read R->L for correct meaning, not L->R.
The solution to the problem was changing the association from hasOne to belongsTo as follows: Request.belongsTo(Vessel), so now the FK will be created on Request.
Quite a confusing choice of association names and semantics!