I want to use DynamoDB for creating tables. We don't have to specify all the column names while creating schema in DyamoDB and only the primary key(hash key + sort key[optional]). Now if my table does have some other attributes that I want to be there for every item inserted-i.e., add NOT NULL constraint to an attribute other than the key, then how can I achieve it in DynamoDB?
There is no NotNull constraint explicitly available on DynamoDB. However there is a feature to provide default value for the attribute if you are using DynamoDBMapper.
Also, DynamoDB API doesn't allow to add an attribute with empty value (i.e. Null or empty string ''). The API does throw an exception.
In other words, you don't need to define a constraint like RDBMS database. Also, there is no workaround to override this functionality. This condition applies to all attributes i.e you can't have any attributes with NULL or empty value.
Example to set default value using annotation :-
#DynamoDBAutoGeneratedDefault("default")
#DynamoDBAttribute(attributeName = "name")
public String getName() {
return name;
}
com.amazonaws.services.dynamodbv2.model.AmazonDynamoDBException:
Supplied AttributeValue is empty, must contain exactly one of the
supported datatypes (Service: AmazonDynamoDBv2; Status Code: 400;
Error Code: ValidationException; Request ID:
1dd8288c-7151-43d3-83d0-dbb7842d705a)
Related
I have a string attribute that can be an empty value. And I want to set it as a Global Secondary Index. But it showed an error when I tried to perform UpdateItemRequest or SaveTable Context:
Amazon.DynamoDBv2.AmazonDynamoDBException: One or more parameter values are not valid. A value specified for a secondary index key is not supported. The AttributeValue for a key attribute cannot contain an empty string value. IndexName: .... IndexKey: ...
What is wrong with my mindset or my settings? I'm new to DynamoDB and had a MongoDB base. If I don't use GSI for this attribute, how to perform a query on that attribute?
I tried
[DynamoDBIgnore] string property;
var operationConfig = new DynamoDBOperationConfig() { };
operationConfig.IsEmptyStringValueEnabled = true;
operationConfig.Conversion = DynamoDBEntryConversion.V2;
but it does not work.
This states that you are setting the value for your GSI PK to an empty string "" which is not supported.
In order to overcome this, you simply remove any value from that attribute, i.e don't set it at all. This allows your index to become sparse in that it will only store data that has a key associated with it.
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.
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 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
Why do these 2 fetches result in a NotFoundException?
ofy().load().type(MyClass.class).id(myClassInstance.getId()).safeGet();
ofy().load().key(myClassInstance.getKey()).safeGet();
But this query returns an entity:
ofy().load().type(MyClass.class).filter("fieldName",myClassInstance.getUserId()).first().get();
Additional info:
MyClass contains a #Parent and #Id field
You aren't specifying the parent key when loading by key.
ofy().load().type(MyClass.class).id(myClassInstance.getId()).safeGet();
// should be:
ofy().load().type(MyClass.class).parent(myClassInstance.getParent()).id(myClassInstance.getId()).safeGet();
For the second line, I suspect your implementation of getKey() is flawed and missing the parent key. The query works because the query is not a key lookup; it just returns whatever is in the index for the property.
Remember that ids are only unique for a particular parent. The unique identifier for an entity is {parent, id}. Read https://code.google.com/p/objectify-appengine/wiki/Concepts carefully.