Working with Lucene Search Index in Sitecore 6. Part III - Code examples

If you read my previous posts about Lucene search index, then you already know how to configure it and how it works in Sitecore application.

In this part we will take a look at API to see what can be achieved using the search index.

To search existing index we need to get an index instance somehow. I'm not going to show the code examples that you would write with old search index. If you're intrested in it, check out this article Lecene Search Engine.

Additional layer of API for new search index resides under Sitecore.Search namespace. In order to get a search index object, you would need to use members of SearchManager class.

To get an index by name use this line of code:

Index indx = Search.Manager.GetIndex(index_name);

If you want to use default system index, you can simply call SystemIndex property of SearchManager class. In order to use Sitecore API to look up for some info in the index, you need to created a search context.

It's easy to do by calling CreateSearchContext method of the index object we got previously. It's also possible to create a search context by using one for the constructors of IndexSearchContext class. In this case it will be easy to run search queries by passing a search index instance as a parameter to the search context.

To search information, we need to create a query and run it in the search context. Sitecore API has a few classes that you can use to build search queries. Let's take a look at each of them:

FullTextQuery - this type of query searches the index by "_content" field. All information from text fields (such as "Single-Line Text", "Rich Text", "Multi-Line Text", "text", "rich text", "html", "memo") is stored there. Data in this field are indexed and tokenized. Which means that the search operations running on these data are very efficient.

FieldQuery - this type of query allows you to search any field that was added to the index. By default database crawler adds all item fields to the index.

CombinedQuery - this type of query was designed to allow you create complex queries with additional conditions. For instance to find items which have specific work in title and belong to some category. When you add search queries to this type of query, you need to supply QueryOccurance parameter. It's Enum type that has the following members:

- Must - it's a logical AND operator in Lucene boolean query.

- MustNot - it's a logical NOT operator in Lucene boolean query.

- Should - it's a logical OR operation in Lucene boolean query.

You can read more about this operators in Query Parser Syntax article.

All of these query types are derived from QueryBase class.

There is one thing left until we jump from the theory to some code samples. To run defined queries, you need to use one of Search methods of IndexSearchContext object.

Now let's create a couple of samples to see a real code that goes behind the theory.

Sample 1: Searching text fields.

// Next samples will skip lines with getting the index instance and creating the search context.

// Get an index object

Index indx = SearchManager.GetIndex("my_index");

// Create a search context

using (IndexSearchContext searchContext = indx.CreateSearchContext())

{

// In following examples I will be using QueryBase class to create search queries.

FullTextQuery ftQuery = new FullTextQuery("welcome");

SearchHits results = searchContext.Search(ftQuery);

}

Sample 2: Searching item fields

Let's say we want to find items classified by some category. There is a trick searching by GUIDs so let's say our category is just a string name.

.....

// FieldQuery ctor accepts two parambers. First is a field name. The other one is a value we're looking for.

QueryBase query = FieldQuery("category", "slr");

SearchHits results = searchContext.Search(query);

.....

Sample 3: Searching by multiple conditions

Turned out that your category parameter is not enough to get required results. You client is screaming that there are too many items and business users cannot find ones they are looking for (is there anything they can find?).

Obviously you have some additional fields that can help to find more strict results. Let's say there is a rating field with values from 1 to 5.

That's where CombinedQuery gets into the game.

.....

// CombinedQuery object has Add method that should be used to add search queries to it. That's why we cannot use base class variable here.

CombinedQuery query = new CombinedQuery();

QueryBase catQuery = new FieldQuery("category", "slr");

QueryBase ratQuery = new FieldQuery("rating", "5");

query.Add(catQuery, QueryOccurance.Must);

query.Add(ratQuery, QueryOccurance.Must);

var hits = searchContext.Search(query);

.....

All results are presented as SearchHits object. Now you should use of following methods of SearchHits object to get the results as Sitecore items:

- FetchResults(int, int) - returns search results as SearchResultCollection. First parameter is a start position of an item you want to start fetching results from. Second one is count of items you want to fetch. By calling this function as mentioned below, you can get all results at once:

var results = hits.FetchResults(0, hits.Length);

- Slice(int) - returns all results as IEnumerable collection.

- Slice(int, int) - this method has similar signature to FetchResults but returns results as IEnumerable collection.

Here are a couple of examples the way you can transform SearchHits object into Sitecore items.

Sample 4: using FetchResults

.....

SearchResultCollection results = hits.FetchResults(0, hits.Length);

IEnumerable searchItems = from hit in results

select hit.GetObject();

}

.....

Sample 5: using Slice

.....

IList searchItems = List();

foreach(var hit in hits.Slice(0))

{

ItemUri itemUri = new ItemUri(hit.Url);

if (itemUri != null)

{

Item item = ItemManager.GetItem(itemUri.ItemID, itemUri.Language, itemUri.Version, Factory.GetDatabase(itemUri.DatabaseName));

if (item != null)

{

searchItems.Add(item);

}

}

}

.....

It's worth to mention that some variations of Search method of IndexSearchContext class can accept Lucene.Net.Search.Query as a search query parameter. It becomes very useful when you need to create a complex query which cannot be built with Sitecore query types.

Searching GUIDs.

New search index has lots of useful built-in fields that help to build strict queries.

Besides standard fields it has the following fields that contain GUIDs in ShortID format:

- _links - contains all references to current item

- _path - contains ShortIDs for every parent item in the path relative to current item

- _template - contains GUID of item's tempalte.

NOTE: this field is supposed to have ShortID value instead of GUID one. This field should not be used in combined queries prior to Sitecore 6.2 releases.

If you decide to add custom fields to your search index and they should have GUID values, you need to store them as ShortID in lower case format. Otherwise search will not be able to find any results. The reason why it happens is because Lucene recognizes GUIDs and applies special parsing for them. It works fine if search query has only one field to look into. If it's combined/complex query then it fails to find anything even if it's correct.

So, remember if you need to filter search results by template, you will have to customize DatabaseCrawler to add another field (e.g. _shorttemplateid) to store item template id in ShortID format.

Sample 1: Find all item references

.....

QueryBase query = FieldQuery("_links", ShortID.Encode(item.ID).ToLowerInvariant());

SearchHits results = searchContext.Search(query);

.....

Sample 6: Find all items based on specified template

.....

// Prior to Sitecore 6.2 release, you will need to add and use _shorttemplateid field

QueryBase query = FieldQuery("_template", ShortID.Encode(item.ID).ToLowerInvariant());

SearchHits results = searchContext.Search(query);

.....

Sample 7: Find items that are descendants of a specified one

.....

QueryBase query = FieldQuery("_path", ShortID.Encode(item.ID).ToLowerInvariant());

SearchHits results = searchContext.Search(query);

.....

Sample 8: Find items of a parent and belong to a specific template

.....

CombinedQuery query = new CombinedQuery();

query.Add(new FieldQuery("_shorttemplateid", ShortID.Encode(templateId).ToLowerInvariant()), QueryOccurance.Must);

query.Add(new FieldQuery("_path", ShortID.Encode(parent.ID).ToLowerInvariant())), QueryOccurance.Must);

.....

That's all I wanted to tell about Lucene search index in Sitecore 6. I hope it will help Lucene beginners to better understand the concept and get up to speed with Lucene search index abilities.

Enjoy!