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.
Related
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 am new to aws dynamodb so pardon for any silly mistake. I was trying to fetch two columns from my Activity table. Also I wanted to fetch only those columns where partition key starts with some specific string. Partition key has format activity_EnrolledStudentName.(e.g Dance_studentName) So I wanted to fetch all those items from table where activity is Dance. I was trying to use the following query:
public List<StudentDomain> getAllStudents(String activity) {
List<StudentDomain> scanResult = null;
DynamoDBUtil dynamoDBUtil = new DynamoDBUtil();
AmazonDynamoDB dynamoDBClient = dynamoDBUtil.getDynamoDBClient();
DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient);
DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();
scanExpression.withProjectionExpression("studentId, ActivitySkills")
.addFilterCondition(STUDENT_PRIMARY_KEY,
new
Condition().withComparisonOperator(ComparisonOperator.BEGINS_WITH)
.withAttributeValueList(new
AttributeValue().withS(activity)));
scanResult = mapper.scan(StudentDomain.class, scanExpression);
return scanResult;
However I am getting the following error when i executed above query.
com.amazonaws.services.dynamodbv2.model.AmazonDynamoDBException: Can not use both expression and non-expression parameters in the same request: Non-expression parameters: {ScanFilter} Expression parameters: {ProjectionExpression} (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: TMS27PABBC2BS3UU7LID731G0FVV4KQNSO5AEMVJF66Q9ASUAAJG)
Can anyone please suggest where I am mistaken and which other query shall i use otherwise?
It's not completely clear what you are trying to achieve but if I understood correctly then you don't need a scan operation for that which actually scans the whole table and afterwords filter the result.
DynamoDB dynamoDB = new DynamoDB(client);
Table table = dynamoDB.getTable("TableName");
QuerySpec spec = new QuerySpec()
.withKeyConditionExpression("studentId = : ActivitySkills")
ItemCollection<QueryOutcome> items = table.query(spec);
Iterator<Item> iterator = items.iterator();
Item item = null;
while (iterator.hasNext()) {
item = iterator.next();
System.out.println(item.toJSONPretty());
}
The filter expression you are using are intented to be used as a filter for secondary attributes and not the range or partition keys. At least this is my interpretation of the documentation
Please read the query documentation http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryingJavaDocumentAPI.html
In .net I specify
QueryOperationConfig queryConfig = new QueryOperationConfig
{
Filter = queryFilter,
IndexName = "PARTNAME-NAME-index",
Limit = 1,
BackwardSearch = desc,
Select = SelectValues.SpecificAttributes,
AttributesToGet = new List<string>
{ "PARTNAME","ID", "NAME","WEIGHT" }
};
But in Query results Attributes order is
WEIGHT, ID, PARTNAME, NAME
In my table PARTNAME is Hashkey, ID is Sortkey, and I have GSI PARTNAME-NAME-index combined of PARTNAME and NAME
How can I specify the needed Attributes order,
or how how are they ordered by default?
Firstly, you are using the legacy AttributesToGet parameter.
This is a legacy parameter. Use ProjectionExpression instead.
Answer:-
DynamoDB doesn't guarantee the order of the attributes in results. Primarily, DynamoDB is a key-value store. You need to get the value for the specific key from the result.
Please note that this is not like SELECT statement on RDBMS. This is a NoSQL database and it is completely different from RDBMS.
Is it possible to add constraint to a dynamodb query expression that states that a GSI should be not null?
Can somebody provide examples.
Is possible to construct a query like the one below?
new DynamoDBQueryExpression<XXX>()
.withHashKeyValues(YYY).withKeyConditionExpression(GSI != NULL);
Note:
Please let me know if this is possible in during query and not during filter time?
if you're like me and you landed on this page while finding the answer to the above question, here's the thread you need to see
How do you query for a non-existent (null) attribute in DynamoDB
The DynamoDB String attribute can't have NULL or empty string.
When you try to insert NULL, the API should throw the below exception:-
java.lang.IllegalArgumentException: Input value must not be null
When you try to insert empty string, the API should throw the below exception:-
com.amazonaws.AmazonServiceException: One or more parameter values were invalid: An AttributeValue may not contain an empty string
If you want to add additional filters on some attributes (i.e. attributes other than hash or range key), you can use the below syntax (i.e. withFilterExpression).
Not equals operator is "<>"
Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>();
eav.put(":val1", new AttributeValue().withS("Some value"));
DynamoDBQueryExpression<XXX> queryExpression = new DynamoDBQueryExpression<XXX>();
queryExpression.withHashKeyValues(hashKeyValues);
queryExpression.withFilterExpression("docType <> :val1").withExpressionAttributeValues(eav);
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.