Database Reference
In-Depth Information
Along with these two primary key conditions, several other add-ons are available for con-
figuring the query. Let me name these one by one:
• Usage of the exclusive start key
• Usage of the query or scan filter
• Usage of limit
• Usage of
Select
to retrieve only specified parameters using the
Attrib-
utesToGet
list
• Usage of consistency
• Usage of index and scanning direction
We will discuss each of these in detail. The first four configurations are common to both
query and scan operations, and the next two configurations are available only for query.
Let's first see how these could be added to the
QueryRequest
instance. Then we will
discuss detailed configurations. Have a look at the following code:
QueryRequest queryRequest = new QueryRequest()
.withTableName("Tbl_Book")
.withKeyConditions(keyConditions)
.withIndexName("Index_Name")
.withScanIndexForward(true)
.withSelect(Select.SPECIFIC_ATTRIBUTES)
.withAttributesToGet(Arrays.asList("BookTitle",
"PubDate"))
.withLimit(10)
.withConsistentRead(true);
We are already familiar with the first two (
with
) methods, which configure the table
name and key conditions to the
QueryRequest
instance. The third parameter specifies
the index through which the query has to be executed. The fourth parameter specifies
whether the search (or query operation) on index should be retrieved in the ascending or-
der;
true
means ascending order,
false
means descending order. By default, the order-
ing is ascending.
The fifth parameter is used to tell
QueryRequest
, which are all the attributes that need
to be retrieved from the table.
Select
is an enumerator just like
ComparisonOper-
ator
, whose possible values are shown as follows:
•
ALL_ATTRIBUTES
: This returns all the item attributes from the table or index.
