Search Tag Data using SQL Query
NCache provides object queries through which you can search and delete result sets based on the criteria given to the query. To retrieve data according to your specified criteria, NCache provides you with an extension of SQL queries. It lets you search the data in your cache based on the requirement. A special keyword $Tag$ is used to specify that the condition under consideration uses Tags. The SQL query with the search criteria is executed using ExecuteReader. The ExecuteReader processes the query on the server-side and then sends the result in chunks (as a dictionary containing keys and values) to the client in a tabular form to the ICacheReader type of instance. You can query an item having a specific Tag as explained below.
Prerequisites
Before using the NCache Client-side APIs, ensure that the following prerequisites are fulfilled:
- Add the following Maven dependencies for your Java client application in
pom.xml file:
<dependency>
<groupId>com.alachisoft.ncache</groupId>
<!--for NCache Enterprise-->
<artifactId>ncache-client</artifactId>
<version>x.x.x</version>
</dependency>
- Install either of the following NuGet packages in your .NET client application:
- Enterprise:
Install-Package Alachisoft.NCache.SDK -Version 4.9.1.0
- Create a new Console Application.
- Make sure that the data being added is serializable.
- Add NCache References by locating
%NCHOME%\NCache\bin\assembly\4.0 and adding Alachisoft.NCache.Web and Alachisoft.NCache.Runtime as appropriate.
- Include the
Alachisoft.NCache.Web.Caching and Alachisoft.NCache.Runtime.Caching namespaces in your application.
- To learn more about the NCache Legacy API, please download the NCache 4.9 documents available as a .zip file on the Alachisoft Website.
Search Data in Cache with One Tag
Using object queries, a single Tag can be used to retrieve all the items associated with that Tag. The following example retrieves all the items associated with the Tag VIP Customers using the SQL query.
Note
Use the fully qualified name (FQN) of the class Customer, e.g., Data.Customer.
try
{
// Precondition: Cache is already connected
// Create a query for search
// Use the Fully Qualified Name (FQN) of your own custom class
string query = "Select CustomerID,ContactName FROM FQN.Customer WHERE $Tag$ = ?";
// Use QueryCommand for query execution
var queryCommand = new QueryCommand(query);
queryCommand.Parameters.Add("$Tag$", "VIP Customers");
// Executing Query
ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);
// Read results if 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 contactName = reader.GetValue<string>("ContactName");
Console.WriteLine($"Customer '{contactName}' having ID '{customerID}' is a VIP Customer.");
}
}
else
{
Console.WriteLine($"No VIP Customers 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
{
// Precondition: Cache is already connected
// Create a query for search
// Use the Fully Qualified Name (FQN) of your custom class
String query = "Select customerID,contactName FROM FQN.Customer WHERE $Tag$ = ?";
// Use QueryCommand for query execution
QueryCommand queryCommand = new QueryCommand(query);
queryCommand.getParameters().put("$Tag$", "VIP Customers");
// Executing Query
CacheReader reader = cache.getSearchService().executeReader(queryCommand);
// Read results if result set is not empty
if (reader.getFieldCount() > 0)
{
while (reader.read())
{
// Get the value of the result set
String customerID = reader.getValue("customerID", String.class);
String contactName = reader.getValue("contactName", String.class);
System.out.println("Customer '" + contactName + "' having ID '" + customerID + "' is a VIP Customer.");
}
} else
{
System.out.println("No VIP Customers found");
}
}
catch (OperationFailedException ex)
{
if (ex.getErrorCode() == NCacheErrorCodes.INCORRECT_FORMAT)
{
// Make sure the query format is correct
}
else
{
// Exception can occur due to:
// Connection Failures
// Operation performed during state transfer
// Operation Timeout
}
}
catch (Exception ex)
{
// Any generic exception like NullPointerException or IllegalArgumentException
}
try:
# Precondition: Cache is already connected
# Create a query for search
# Use the Fully Qualified Name (FQN) of your own custom class
query = "SELECT $Value$ FROM FQN.Customer WHERE $Tag$ = ?"
# Use QueryCommand for query execution
query_command = QueryCommand(query)
query_command.set_parameters({"$Tag$": "VIP Customers"})
# Executing Query
reader = cache.get_search_service().execute_reader(query_command)
# Read results if result set is not empty
if reader.get_field_count() > 0:
while reader.read():
result = reader.get_value(Customer, 1)
# Perform operations
else:
print("No VIP Customers found")
except Exception as error:
# Exception can occur due to:
# Connection Failures
# Operation Timeout
# Operation during state transfer
print("An error occurred:", str(error))
try
{
// Precondition: Cache is already connected
// This is an async method
// Create a query for search
// Use the Fully Qualified Name (FQN) of your own custom class
const query = "SELECT $Value$ FROM FQN.Customer WHERE $Tag$ = ?";
// Use QueryCommand for query execution
const queryCommand = new ncache.QueryCommand(query);
const paramMap = new Map();
paramMap.set("$Tag$", "VIP Customers");
queryCommand.setParameters(paramMap);
// Executing Query
const searchService = await this.cache.getSearchService();
const reader = await searchService.executeReader(queryCommand);
// Read results if result set is not empty
if (reader.getFieldCount() > 0)
{
let hasRow = await reader.read();
while (hasRow)
{
const val = reader.getValue(1, JsonDataType.Object);
// Perform Operations
}
}
else
{
console.log("No VIP Customers found");
}
}
catch(error)
{
// Handle errors
}
// Using NCache Enterprise 4.9.1
try
{
// Precondition: Cache is already connected
// Create a query for search
// Use the Fully Qualified Name (FQN) of your own custom class instead of Customer in the query string
string query = "SELECT FQN.Customer WHERE this.$Tag$=?";
Hashtable queryValue = new Hashtable();
// Add items to cache containing Tags in ArrayList if multiple Tags value is required
ArrayList queryTagList = new ArrayList();
queryTagList.Add("VIP Customers");
// Add Tag list to Hashtable for query searching values.
queryValue.Add("$Tag$", queryTagList);
// Executing Query
ICacheReader queryResult = cache.ExecuteReader(query, queryValue, true);
// queryResult contains all keys related to both Tags
if (queryResult.FieldCount > 0)
{
while (queryResult.Read())
{
// Get the value of the result set
var customerobj = queryResult.GetValue(1);
if (customerobj is Customer customer)
{
Console.WriteLine($"Customer '{customer.CompanyName}' having ID '{customer.CustomerID}' is a VIP Customer.");
}
}
}
else
{
Console.WriteLine($"No VIP Customers 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
}
Warning
Providing a Null Tag value for the query will throw an ArgumentNullException or NullPointerException.
In order to get more details on NCache queries, please refer to the SQL Reference for NCache section.
Note
To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.
Additional Resources
NCache provides sample application for Tags on GitHub.
See Also
.NET: Alachisoft.NCache.Runtime.Caching namespace.
Java: com.alachisoft.ncache.runtime.caching namespace.
Python: ncache.runtime.caching class.
Node.js: Tag class.
