I have a table with a primary key and a sort key; since this is a composite key, I have multiple primary keys mapped with different sort keys.
How can I get all of the sort keys associated with a particular primary key?
I tried using the "Get" operation, but that seems to expect the sort key as well (even though these are what I'm looking for). I also looked at the "BatchGet" operation, but this is for multiple different keys, not for a single primary key with multiple different sort keys.
I tried to do "query" as well and wasn't successful, but I understand this less, so it's possible this is the solution -- is that the case? I am also aware that I could "scan" the entire database and specifically find all items with that particular primary key, but I'm looking to avoid this if possible.
I am working with JS and using this as a reference: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html.
Thank you!
Query() is what you want...
Basically, you just query the table (or index) with a keycondition of HashKey = :hkey and leave off any AND of sort key conditions...
In the docs you linked to, there's a section for query modifying that example...
var params = {
TableName: 'Table',
KeyConditionExpression: 'HashKey = :hkey',
ExpressionAttributeValues: {
':hkey': 'key'
}
};
var documentClient = new AWS.DynamoDB.DocumentClient();
documentClient.query(params, function(err, data) {
if (err) console.log(err);
else console.log(data);
});
Related
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 fairly new in this realm and any help is appreciated
I have a table in Dynamodb database named Tenant as below:
"TenantId" is the hash primary key and I have no other keys. And I have a field named "IsDeleted" which is boolean
Table Structure
I am trying to run a query to get the record with specified "TenantId" while it is not deleted ("IsDeleted == 0")
I can get a correct result by running the following code: (returns 0 item)
var filter = new QueryFilter("TenantId", QueryOperator.Equal, "2235ed82-41ec-42b2-bd1c-d94fba2cf9cc");
filter.AddCondition("IsDeleted", QueryOperator.Equal, 0);
var dbTenant = await
_genericRepository.FromQueryAsync(new QueryOperationConfig
{
Filter = filter
}).GetRemainingAsync();
But no luck when I try to get it with following code snippet (It returns the item which is also deleted) (returns 1 item)
var queryFilter = new List<ScanCondition>();
var scanCondition = new ScanCondition("IsDeleted", ScanOperator.Equal, new object[]{0});
queryFilter.Add(scanCondition);
var dbTenant2 = await
_genericRepository.LoadAsync("2235ed82-41ec-42b2-bd1c-d94fba2cf9cc", new DynamoDBOperationConfig
{
QueryFilter = queryFilter,
ConditionalOperator = ConditionalOperatorValues.And
});
Any Idea why ScanCondition has no effect?
Later I also tried this: (throw exception)
var dbTenant2 = await
_genericRepository.QueryAsync("2235ed82-41ec-42b2-bd1c-d94fba2cf9cc", new DynamoDBOperationConfig()
{
QueryFilter = new List<ScanCondition>()
{
new ScanCondition("IsDeleted", ScanOperator.Equal, 0)
}
}).GetRemainingAsync();
It throws with: "Message": "Must have one range key or a GSI index defined for the table Tenants"
Why does it complain about Range key or Index? I'm calling
public AsyncSearch<T> QueryAsync<T>(object hashKeyValue, DynamoDBOperationConfig operationConfig = null);
You simply cant query a table only giving a single primary key (only hash key). Because there is one and only one item for that primary key. The result of the Query would be that still that single item, which is actually Load operation not Query. You can only query if you have composite primary key in this case (Hash (TenantID) and Range Key) or GSI (which doesn't impose key uniqueness therefore accepts duplicate keys on index).
The second code attempts to filter the Load. DynamoDBOperationConfig's QueryFilter has a description ...
// Summary:
// Query filter for the Query operation operation. Evaluates the query results and
// returns only the matching values. If you specify more than one condition, then
// by default all of the conditions must evaluate to true. To match only some conditions,
// set ConditionalOperator to Or. Note: Conditions must be against non-key properties.
So works only with Query operations
Edit: So after reading your comments on this...
I dont think there conditional expressions are for read operations. AWS documents indicates they are for put or update operations. However, not being entirely sure on this since I never needed to do a conditional Load. There is no such thing like CheckIfExists functionality as well in general. You have to read the item and see if it exists. Conditional load will still consume read throughput so your only advantage would be only NOT retrieving it in other words saving the bandwith (which is very negligible for single item).
My suggestion is read it and filter it in your application layer. Dont query for it. However what you can also do is if you very need it you can use TenantId as hashkey and isDeleted for range key. If you do so, you always have to query when you wanna get a tenant. With the query you can set rangeKey(isDeleted) to 0 or 1. This isnt how I would do it. As I said, would just read it and filter it at my application.
Another suggestion thing could be setting a GSI on isDeleted field and writing null when it is 0. This way you can only see that attribute in your table when its only 1. GSI on such attribute is called sparse index. Later if you need to get all the tenants that are deleted (isDeleted=1) you can simply scan that entire index without conditions. When you are writing null when its 0 dynamoDB wont put it in the index at the first place.
i have 100 records in collection,
collection name:'users'
{
"name":'senthilkumar',
"email":'senthily88#gmail.com', //HashKey
"age":21,
"created":1465733486137, //RangeKey-timestamp
}
i need to fetch records the following sql query wise
select * from users order by created desc limit 10
How i can get above query format records from DynamoDB
Dynamodb sorts the results by the range key attribute. You can set the ScanIndexForward boolean parameter to true for ascending or false for descending.
resource: http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
Use the KeyConditionExpression parameter to provide a specific value
for the partition key. The Query operation will return all of the
items from the table or index with that partition key value. You can
optionally narrow the scope of the Query operation by specifying a
sort key value and a comparison operator in KeyConditionExpression.
You can use the ScanIndexForward parameter to get results in forward
or reverse order, by sort key.
To Save Json Data to DynamoDB us put()
var Newparams = {
TableName: this.SuffleTableName,
Item: {
"userId": /* YOUR PRIMARY KEY */,
"addedAt": /* YOUR SORT KEY */,
"status": /* Additional Datas */,
}
}
Fetch Data From DynamoDB using Query()
QueryParam = {
TableName: 'YOUR TABLE NAME HERE',
IndexName: 'YOUR INDEX NAME HERE', //IF YOUR CREATED NEW INDEX
KeyConditionExpression: "UserId = :UserId ", //YOUR PRIMARY KEY
ExpressionAttributeValues: {
":UserId": UserId,
},
ScanIndexForward: false, //DESC ORDER, Set 'true' if u want asc order
ExclusiveStartKey: LastEvalVal, //Pagination - LastEvaluatedKeyPair
Limit: 10 //DataPerReq
}
If you want to return all rows in your table, you cannot use the query API, because that API requires you to provide a partition key value to filter your results by (i.e. assuming that your partition key is name you would only be able to use the query API to bring back the subset of results that have name = a given value, i.e. name= senthilkumar
If you want to return all rows in your table, you must use the Scan API: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SQLtoNoSQL.ReadData.Scan.html
Note that all results will be provided in ascending order by the value of the Range Key. You cannot reverse sort the contents with the Scan API. You would need to reverse your resultset in the application tier using whatever language you're writing your code in to turn the results upside down.
Scan does not scale well and it is not possible to use Scan to create a paginated, reverse sorted solution if your table contains items with unique partition keys.
If this is your situation, and if you want to return paginated + reverse sorted sets back from DynamoDB, you will need to re-consider the design of your table and which columns are the partition key/range key/index so that you can use the Query API.
I am writing an app using the Realm.io database that will pull data from another, server database. The server database has some tables whose primary keys are composed of more than one field. Right now I can't find a way to specify a multiple column key in realm, since the primaryKey() function only returns a String optional.
This one works:
//index
override static func primaryKey() ->String?
{
return "login"
}
But what I would need looks like this:
//index
override static func primaryKey() ->[String]?
{
return ["key_column1","key_column2"]
}
I can't find anything on the docs on how to do this.
Supplying multiple properties as the primary key isn't possible in Realm. At the moment, you can only specify one.
Could you potentially use the information in those two columns to create a single unique value that you could use instead?
It's not natively supported but there is a decent workaround. You can add another property that holds the compound key and make that property the primary key.
Check out this conversation on github for more details https://github.com/realm/realm-cocoa/issues/1192
You can do this, conceptually, by using hash method drived from two or more fields.
Let's assume that these two fields 'name' and 'lastname' are used as multiple primary keys. Here is a sample pseudo code:
StudentSchema = {
name: 'student',
primaryKey: 'pk',
properties: {
pk: 'string',
name: 'string',
lastname: 'string',
schoolno: 'int'
}
};
...
...
// Create a hash string drived from related fields. Before creating hash combine the fields in order.
myname="Uranus";
mylastname="SUN";
myschoolno=345;
hash_pk = Hash( Concat(myname, mylastname ) ); /* Hash(myname + mylastname) */
// Create a student object
realm.create('student',{pk:hash_pk,name:myname,lastname:mylastname,schoolno: myschoolno});
If ObjectId is necessary then goto Convert string to ObjectID in MongoDB
How to query range key programmatically in DynamoDB, I am using .Net AWSSDK ,I am able to query on Hash key with below code :
GetItemRequest request = new GetItemRequest
{
TableName = tableName
};
request.Key = new Dictionary<string,AttributeValue>();
request.Key.Add("ID",new AttributeValue { S = PKValue });
GetItemResponse response = client.GetItem(request);
Please suggest,
Thanks in advance.
There are two kinds of primary key in DynamoDB: Hash-only or Hash-Range.
In the above code I guess your table is Hash-only and you use the hash key to retrieve an element with hashkey equals to PKValue.
If your table is in H-R schema and you want to retrieve a specific element with a hashKey and rangeKey, you can reuse the above code and in addition, add the {"RangeKey", new AttributeValue } into your your request.KEY
On the other hand, query means a different thing in DynamoDB. Query will return you a list of rows sorted in some order.