SQL Search for Objects Syntax and Usage

Note

This feature is only available in NCache Enterprise Edition.

NCache provides you a list of data retrieval options including selected projections as well as whole cache items along with the keys. Using an SQL-like query syntax, you can easily retrieve selected projections, all projections(using *), Groups, Named Tags etc. This is done through ExecuteReader() which returns the result set in a tabular form to ICacheReader type of instance. Column count and attribute values can be fetched through their names or through index number from ICacheReader. Make sure the instance of ICacheReader is always closed after execution, as it is necessary to clean the resources.

The new query syntax allows you to retrieve specific projections from the cache store. Also, you can now specify * to retrieve the whole data of a type from the cache.

Indexing for searchable objects and their attributes need to be configured first as explained in Configuring Query Indexes in Administrator's Guide.
Include the following namespaces in your application:
- Alachisoft.NCache.Client
- Alachisoft.NCache.Runtime.Caching
- Alachisoft.NCache.Client.Services
- Alachisoft.NCache.Runtime.Exceptions
The application must be connected to cache before performing the operation.
Cache must be running.
Make sure that the data being added is serializable.
To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Include the following namespaces in your application:
- import com.alachisoft.ncache.web.caching.*;
- import com.alachisoft.ncache.runtime.exceptions.*;
The application must be connected to cache before performing the operation.
Cache must be running.
Make sure that the data being added is serializable.
To ensure the operation is fail safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Modern Syntax

SELECT "*"

Below-mentioned is an example which retrieves all the types from the cache through the * operator.

try
{
    // Pre-condition: Cache is already connected
    // Items are already present in the cache.

    // Provide Fully Qualified Name (FQN) of your custom class 
    string query = "SELECT * FROM FQN.Product WHERE ProductID > ?";

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

    // Providing parameters for query
    queryCommand.Parameters.Add("ProductID",50000);

    // Executing QueryCommand through ICacheReader
    ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

    // Check if the result set is not empty
    if (reader.FieldCount > 0)
    {
        while (reader.Read())
        {
            string result = reader.GetValue<string>("ProductID");

            // Perform operations
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
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
}

SELECT Column Name

Below mentioned is an example which retrieves ProductName column from the cache.

try
{
    // Pre-condition: Cache is already connected
    // Items are already present in the cache.

    // Provide Fully Qualified Name (FQN) of your custom class 
    string query = "SELECT ProductName FROM FQN.Product WHERE ProductID > ?";

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

    // Providing parameters for query
    queryCommand.Parameters.Add("ProductID",50000);

    // Executing QueryCommand through ICacheReader
    ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

    // Check if the result set is not empty
    if (reader.FieldCount > 0)
    {
        while (reader.Read())
        {
            string result = reader.GetValue<string>("ProductName");

            // Perform operations
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
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 performed during state transfer
        // Operation Timeout
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentException, ArgumentNullException
}

SELECT Multiple Columns

In addition to specific column projections, you can also retrieve multiple projections. Below-mentioned is an example which projects $GROUP$ and $Value$ in a single query.

try
{
    // Pre-condition: Cache is already connected
    // Items are already present in the cache.

    // Provide Fully Qualified Name (FQN) of your custom class 
    // Assume that the Product entered is associated to a group
    string query = "SELECT $Value$, $Group$ FROM FQN.Product WHERE ProductID > ?";

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

    // Providing parameters for query
    queryCommand.Parameters.Add("ProductID",50000);

    // Executing QueryCommand through ICacheReader
    ICacheReader reader = cache.SearchService.ExecuteReader(queryCommand);

    // Check if the result set is not empty
    if (reader.FieldCount > 0)
    {
        while (reader.Read())
        {
            // reader.GetValue(0) = Cache key
            Product value = reader.GetValue<Product>(1);
            string groupName = reader.GetValue<string>(2);         
            // Perform operations
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
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 performed during state transfer
        // Operation Timeout
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentException, ArgumentNullException
}

Legacy Syntax

Note

Legacy API is only available in NCache Enterprise Edition.

The following example creates a query which searches the cache according to the given criteria, executes it using ExecuteReader and then returns the values of the result set. The criteria being used is the UnitsInStock being greater than 10. For Java, the searchEntries method is used to search for keys and values in the cache.

.NET/.NET Core
Java

try
{
    // Pre-condition: Cache is already connected
    // Items are already present in the cache.

    // Create a query which will be executed on the data set
    // Use the Fully Qualified Name (FQN) of your own custom class
    string query = "SELECT FQN.Product WHERE this.ProductID > ?";

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

    // Providing parameters for query
    queryCommand.Parameters.Add("ProductID",50000);

    // Executing QueryCommand through ICacheReader
    ICacheReader reader = cache.ExecuteReader(queryCommand);

    // Check if the result set is not empty
    if (reader.FieldCount > 0)
    {
        while (reader.Read())
        {
            Product result = reader.GetValue<"ProductID">(1);
            // Perform operations
        }
    }
    else
    {
        // Null query result set retrieved
    }
}
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 performed during state transfer
        // Operation Timeout
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentException, ArgumentNullException
}

try
{    
    // Pre-condition: Cache is already connected
    // Items are already present in the cache.

    // Create a query which will be executed on the data set
    // Use the Fully Qualified Name (FQN) of your own custom class
    string query = "SELECT Product where this.ProductID > ?";

    // Providing parameters for query
    HashMap values = new HashMap();
    values.put("ProductID", 50000);

    HashMap items = new HashMap();
    items = cache.searchEntries(query, values);

    // Check if the result set is not empty
    if(items.size() > 0)
    {
        // Perform operations using the retrieved objects
    }
}
catch (Exception ex) 
{
    // Exception can occur due to:
    // Connection Failures
    // Operation Timeout
    // Operation performed during state transfer
    // Any generic exception
}

Recommendation: 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 SQL Searching at:

GitHub
Shipped with NCache: %NCHOME%\samples\dotnet\SearchUsingSQL

SQL Search for Objects Syntax and Usage

Note

Pre-Requisites

Modern Syntax

SELECT "*"

SELECT Column Name

SELECT Multiple Columns

Legacy Syntax

Note

Additional Resources

See Also