You can use the collapse feature to collapse the result set based on a specified column when the results of a query contain large amounts of data of a specific type. Data of the corresponding type is displayed only once in the query results to ensure diversity in the result types.

Prerequisites

  • The OTSClient instance is initialized. For more information, see Initialization.
  • A data table is created and data is written to the table.
  • A search index is created for the table. For more information, see Create search indexes.

Usage notes

  • If you use the collapse feature, you must implement pagination by specifying offset and limit instead of Token.
  • If you aggregate and collapse a result set at the same time, the result set is aggregated before it is collapsed.
  • If you collapse the query results, the total number of groups of the returned results is determined by the sum of the offset and limit values. A maximum of 10,000 groups can be returned.
  • The total number of rows returned in the results indicates the number of returned rows before you use the collapse feature. After the result set is collapsed, the total number of the returned groups cannot be queried.

Parameters

Parameter Description
query The query type. You can set this parameter to any query type.
collapse The collapse parameter, including the fieldName field.

fieldName: the name of the column based on which the result set is collapsed. Only columns whose values are of the INTEGER, FLOATING-POINT or KEYWORD type are supported.

offset The position from which the current query starts.
limit The maximum number of rows that the current query returns.

To query only the number of matched rows without returning specific data, you can set limit to 0. Then, Tablestore returns the number of matched rows without data from the table.

getTotalCount Specifies whether to return the total number of rows that match the query conditions. By default, this parameter is set to false, which indicates that the total number of rows that match the query conditions is not returned.

Query performance is affected when this parameter is set to true.

tableName The name of the table.
indexName The name of the search index.
columnsToGet Specifies whether to return all columns of each matched row. You can configure returnAll and columns for this parameter.

By default, returnAll is set to false, which indicates that not all columns are returned. If returnAll is set to false, you can use columns to specify the columns to return. If you do not specify the columns to return, only the primary key columns are returned.

If returnAll is set to true, all columns are returned.

Examples

private static void UseCollapse(SyncClient client){
    SearchQuery searchQuery = new SearchQuery(); // Specify the query conditions.
    MatchQuery matchQuery = new MatchQuery();
    matchQuery.setFieldName("user_id");
    matchQuery.setText("00002");

    searchQuery.setQuery(matchQuery);
    Collapse collapse = new Collapse("product_name"); // Collapse the result set based on the product_name values.
    searchQuery.setCollapse(collapse);

    searchQuery.setOffset(1000);
    searchQuery.setLimit(20);
    //searchQuery.setGetTotalCount(true);// Specify that the total number of matched rows is returned.

    SearchRequest searchRequest = new SearchRequest("sampleTable", "sampleSearchIndex", searchQuery);// Specify the names of the table and the search index.    // You can set the columnsToGet parameter to specify the columns to return or specify that all columns are returned. If you do not set this parameter, only the primary key columns are returned.
    //SearchRequest.ColumnsToGet columnsToGet = new SearchRequest.ColumnsToGet();
    //columnsToGet.setReturnAll(true); // Set ReturnAll to true to return all columns.
    //columnsToGet.setColumns(Arrays.asList("ColName1","ColName2")); // Set Columns to return specified columns.
    //searchRequest.setColumnsToGet(columnsToGet);

    SearchResponse response = client.search(searchRequest);  
    //System.out.println(response.getTotalCount());    
    //System.out.println(response.getRows().size()); // Display the number of product types based on the product_name values.
    System.out.println(response.getRows().size()); // Display the product names based on the product_name values.
}