Query JSON Data in Cache

Note

This feature is available in NCache Enterprise edition only.

You can query data using query indexes (as we've detailed in the steps below) or using searchable attributes associated with it. The searchable attributes include:

  • Tags
  • NamedTags
  • Groups

Prerequisites

Step 1: Defining JSON Indexes for Querying Data

To query data using indexes, index your query objects as detailed in our Administrators Guide using the NCache Manager or PowerShell cmdlet. Where you will have to specify a type name or class (such as Alachisoft.NCache.Customer), along with the attributes you will query later (e.g., CompanyName).

Step 2: Specify Type Information for JSON Index Queries

You must provide a type name (the same type name as in the index you've defined previously) to query the JsonObject when adding this object to the cache. Otherwise, you will not be able to perform any queries successfully. You can learn how to specify this type information in your code snippet in our section on Adding JsonObject to Cache with Type Name

Steps 3: Query JsonObjects Using JSON Query Indexes

If you have completed the previous two steps, after which you can search according to the attribute you require (e.g., CompanyName), as demonstrated in the code snippets below. It is necessary to add type information to ensure proper deserialization and validation of the retrieved object from the cache.

// Preconditions:
// (1) Cache is already connected
// (2) Cache is JSON serialized
try
{
    // Retrieve the CacheItem using the CompanyName with a query
    string query = "SELECT * FROM Alachisoft.NCache.Customer WHERE $CompanyName$ = ?";
    var queryCommand = new QueryCommand(query);
    queryCommand.Parameters.Add("$CompanyName$", "CustomerItem");
    var queryResult = cache.SearchService.ExecuteReader(queryCommand);

    // QueryResult contains all the keys and metadata of result
    if (queryResult.FieldCount > 0)
    {
        while (queryResult.Read())
        {
            // Perform operation according to your logic
        }
    }
    else
    {
        // No data containing the given CompanyName exist
    }
}
catch (OperationFailedException ex)
{
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}
Note

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

Query JsonObjects with Groups, Tags, or Named Tags

You can add JsonObject in your cache as a CacheItem. CacheItem is a custom class provided by NCache which can be used to add data to the cache. CacheItem lets you add various properties to it, e.g, Locking, Dependency, Tags, NamedTags and Groups.

Warning

An attribute cannot contain a reference to the object itself. If done so, an exception is thrown.

The following example adds a CacheItem to the cache with JsonObject Product as the value of the CacheItem. Tags are added to the CacheItem and then item is fetched using the tag using a query command.

Customer customer = FetchCustomerFromDB(1001);

// Create a unique key for the object
string key = $"Customer:{customer.CustomerID}";

// Create a new JSON object and set attributes
// string values need to be added with JsonValue
var jsonCustomer = new JsonObject("Alachisoft.NCache.Customer");
jsonCustomer.AddAttribute("CustomerID", customer.CustomerID);
jsonCustomer.AddAttribute("ContactName", (JsonValue)customer.ContactName);
jsonCustomer.AddAttribute("CompanyName", (JsonValue)customer.CompanyName);
jsonCustomer.AddAttribute("Phone", customer.Phone);
jsonCustomer.AddAttribute("Address", customer.Address);

// Create a new CacheItem
var item = new CacheItem(jsonCustomer);

// Add Tag to the cacheItem
item.Tags = new Tag[] { new Tag("CustomerItem") };

// Add CacheItem in the cache with the value
cache.Insert(key, item);

// Retrieve the CacheItem using the tag with a query
string query = "SELECT * FROM Alachisoft.NCache.Customer WHERE $Tag$ = ?";
var queryCommand = new QueryCommand(query);
queryCommand.Parameters.Add("$Tag$", "CustomerItem");
var queryResult = cache.SearchService.ExecuteReader(queryCommand);

// QueryResult contains all the keys and metadata of result
if (queryResult.FieldCount > 0)
{
    while (queryResult.Read())
    {
        // Perform operation according to your logic
    }
}
else
{
    // No data containing the named tag(s) exist
}

Additional Resources

NCache provides sample application for Cache Data as JSON on GitHub.

See Also

Overview
Using JsonObject in Cache
Cache Serialization Format