Search Cache Data with Named Tags and SQL

Note

This feature is only available in NCache Enterprise Edition.

The Object Queries can also be used to retrieve items from the cache with your query criteria being named tags. The query when executed will search the cache according to the named tag provided in the SQL query. Before searching, make sure that the item is added to the cache with the named tags. Refer to the Add Items with Named Tags section to get a detail on creating and adding named tags.

Prerequisites

To learn about the standard prerequisites required to work with all NCache client side features please refer to the given page on Client Side API Prerequisites.
Custom classes/searchable attributes must be indexed as explained in Configuring Query Indexes.
For API details, refer to: ICache, ICacheReader, QueryCommand, ExecuteReader, SearchService.

Syntax

The following example retrieves the Products from the cache where the values of named tags match the provided value.

try
{
    // Pre-conditions: Cache is already connected

    /* User wants to see the details of all the customers having 12% VIP membership discount using SQL query.
    Custom class is query indexed through the NCache Manager or config.ncconf*/

    // Create an SQL Query with the specified criteria
    // Make sure to use the Fully Qualified Name for custom class
    string query = "SELECT CustomerID,ContactName FROM Alachisoft.NCache.Samples.Data.Customer WHERE VIP_Membership_Discount = 0.12 ";

    // Use QueryCommand for query execution
    var queryCommand = new QueryCommand(query);

    // Executing the Query
    ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

    // Read results if the result set is not empty
    if (reader.FieldCount > 0)
    {
        while (reader.Read())
        {
            // Get the value of the result set
            string customerID = reader.GetValue<string>("CustomerID");
            string customerName = reader.GetValue<string>("ContactName");

            Console.WriteLine($"Customer '{customerName}' with ID '{customerID}' has VIP membership discount.");
        }
    }
    else
    {
        Console.WriteLine($"No VIP members found");
    }
}
catch (OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures 
        // Operation Timeout
        // Operation performed during state transfer    
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentException, ArgumentNullException    
}

try
{
    // Pre-conditions: Cache is already connected
    // Items are already present in the cache with named tags
    // Custom class is query indexed through NCache Web Manager or config.ncconf
    // Create SQL Query with the specified criteria
    // Make sure to use the Fully Qualified Name (FQN)
    String query = "SELECT $Value$ FROM FQN.Product WHERE FlashSaleDiscount = ?";

    // Use QueryCommand for query execution
    QueryCommand queryCommand = new QueryCommand(query);

    queryCommand.getParameters().put("FlashSaleDiscount", 0.5);

    // Executing query
    CacheReader reader = cache.getSearchService().executeReader(queryCommand);

    // Check if result set is not empty
    if (reader.getFieldCount() > 0)
    {
        while (reader.read())
        {
            // Get the value of the result set
            Product result = reader.getValue(1,Product.class);
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
catch (OperationFailedException ex)
{
    if (ex.getErrorCode() == NCacheErrorCodes.INCORRECT_FORMAT)
    {
        // Make sure that the query format is correct
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
    // Any generic exception like IllegalArgumentException or NullPointerException 
}

try {
    // Pre-conditions: Cache is already connected
    // Items are already present in the cache with named tags
    // Custom class is query indexed through NCache Web Manager or config.ncconf
    // Create SQL Query with the specified criteria
    // Make sure to use the Fully Qualified Name (FQN)
    val query = "SELECT $Value$ FROM FQN.Product WHERE FlashSaleDiscount = ?"

    // Use QueryCommand for query execution
    val queryCommand = new QueryCommand(query)

    queryCommand.setParameters(Map("FlashSaleDiscount" -> 0.5))

    // Executing query
    val reader = cache.getSearchService.executeReader(queryCommand)

    // Check if result set is not empty
    if (reader.getFieldCount > 0) while ( {
      reader.read
    }) { // Get the value of the result set
      val result = reader.getValue(1, classOf[Product])
    }
    else {
      // Null query result set retrieved
    }
}
catch {
    case exception: Exception => {
      // Handle any errors
    }
}

// This is an async method
try 
{   
    // Pre-conditions: Cache is already connected
    // Items are already present in the cache with named tags
    // Custom class is query indexed through NCache Web Manager or config.ncconf
    // Create SQL Query with the specified criteria
    // Make sure to use the Fully Qualified Name (FQN)
    var query = "SELECT $Value$ FROM FQN.Product WHERE FlashSaleDiscount = ?";

    // Use QueryCommand for query execution
    var queryCommand = new ncache.QueryCommand(query);

    let parameter = new Map();
    parameter.set("FlashSaleDiscount", 0.5);
    queryCommand.setParameters(parameter);

    // Executing query
    var searchService = await this.cache.getSearchService();

    var reader = await searchService.executeReader(queryCommand);

    // Check if result set is not empty
    if (reader.getFieldCount() > 0)
    {
        while (reader.read())
        {
            // Get the value of the result set
            var result = reader.getValue(1, ncache.JsonDataType.Object);
        }
    }
    else
    {
        // Null query result set retrieved
    }

} catch (error)
{
    // Handle errors
}

try:
    # Pre-conditions: Cache is already connected
    # Items are already present in the cache with named tags
    # Custom class is query indexed through NCache Web Manager or config.ncconf

    # Create SQL Query with the specified criteria
    # Make sure to use the Fully Qualified Name(FQN)
    query = "SELECT $Value$ FROM FQN.Product WHERE FlashSaleDiscount = ?"

    # Use QueryCommand for query execution
    query_command = ncache.QueryCommand(query)

    parameter = {"FlashSaleDiscount": 0.5}
    query_command.set_parameters(parameter)

    # Executing query
    search_service = cache.get_search_service()
    reader = search_service.execute_reader(query_command)

    # Check if result set is not empty
    if reader.get_field_count() > 0:
        while reader.read():
            # Get the value of the result set
            result = reader.get_value(Product, 1)
    else:
        # None query result set retrieved
        print("Query result is None")
except Exception as exp:
    # Handle errors

Note

To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Warning

If you have multiple applications that are sharing the same cache and all of them are supposed to add named tags, then make sure that same named tags have homogenous data types. For e.g. if one client is adding a named tag ProductID with a string data type, then all other clients should add values of ProductID only in a string format for the same cache.

In order to get more detail on object queries please refer to the SQL Reference for NCache section.

Additional Resources

NCache provides sample application for Tags on GitHub.

Search Cache Data with Named Tags and SQL

Note

Prerequisites

Syntax

Note

Warning

Additional Resources

See Also