Table of Contents

Querying by Property

Index a property in the ScaleOut service using the [SossIndex] attribute. Indexed properties can then be used in a LINQ Where clause.

Procedure

  1. Add a using Scaleout.Client.QuerySupport directive to the top of a C# source file to gain access to query extension methods and attributes.

  2. Mark a property with the [SossIndex] attribute to index it in the ScaleOut service.

    • Multiple properties in a class can be indexed.
    • Pass HighPriorityHashable into the attribute's constructor to improve query performance. Up to 8 properties in a class can be added to the service's hashed indexes.
    class UserInfo
{
    public int UserId { get; set; }

    [SossIndex(HashIndexPriority.HighPriorityHashable)]
    public string ZipCode { get; set; }
}

  3. Indexes in the ScaleOut service are updated when objects are added or updated in a cache.

    var conn = GridConnection.Connect("bootstrapGateways=localhost:721");
var cache = new CacheBuilder<int, UserInfo>("user cache", conn).Build();

// Add users
cache.Add(key: 1, new UserInfo { UserId = 1, ZipCode = "12345" });
cache.Add(key: 2, new UserInfo { UserId = 2, ZipCode = "54321" });

  4. Use the QueryObjects() method to create a LINQ expression and query the ScaleOut Service.

    var queryResult = cache.QueryObjects()
                       .Where(user => user.ZipCode == "54321");

foreach (var user in queryResult)
    Console.WriteLine(user.ZipCode);

// Output: 54321

  5. If only the cache keys need to be retrieved from the query, use the SelectKeys operator to return the object's key instead of its value in the cache.

    var justKeys = cache.QueryObjects()
                    .Where(user => user.ZipCode == "12345")
                    .SelectKeys(cache);

foreach (var cacheKey in justKeys)
    Console.WriteLine(cacheKey);

// Output: 1