AWS DynamoDB iOS查询

Question

I followed the tutorial from the official AWS guide, but what is not explained is how to query for secondary indexes, ones I created myself. So what method would I call on queryExpression and how would I use the method (what would I do exactly if I have say three secondary indexes and they each should have a given value for the query)?

Answer 1

From the AWS DynamoDB IOS developers Guide:

http://docs.aws.amazon.com/mobile/sdkforios/developerguide/dynamodb_om.html

The Query API enables you to query a table or a secondary index. You must provide a hash key value in AWSDynamoDBQueryExpression. To query an index, you must also specify the indexName. You must specify the hashKeyAttribute if you query a global secondary with a different hashKey. If the table or index has a range key, you can optionally refine the results by providing a range key value and a condition. The query:expression: method takes two parameters—the class of the resulting object and an instance of AWSDynamoDBQueryExpression. In the following example, we query the Books index table to find all books with author of “John Smith” and price less than 50:

And it would be something like this:

AWSDynamoDBQueryExpression *queryExpression = [AWSDynamoDBQueryExpression new];

queryExpression.indexName = @"Author-Price-index";

queryExpression.hashKeyAttribute = @"Author";
queryExpression.hashKeyValues = @"John Smith";

queryExpression.rangeKeyConditionExpression = @"Price < :val";
queryExpression.expressionAttributeValues = @{@":val":@50};

[[dynamoDBObjectMapper query:[Book class]
          expression:queryExpression]
continueWithBlock:^id(AWSTask *task) {
     if (task.error) {
         NSLog(@"The request failed. Error: [%@]", task.error);
     }
     if (task.exception) {
         NSLog(@"The request failed. Exception: [%@]", task.exception);
     }
     if (task.result) {
         AWSDynamoDBPaginatedOutput *paginatedOutput = task.result;
         for (Book *book in paginatedOutput.items) {
             //Do something with book.
         }
     }
     return nil;
 }];