Go-Solr

An Apache Solr library written in Go, which is my first Go project! Functionality includes:

• Select queries
• Raw Select tqueries - useful for more complex queries such as Function Queries
• Update queries (add/replace/delete)
• Faceting

For more information on Solr itself, please refer to Solr's wiki.

This library is released under the "do whatever you like" license.

Examples / Documentation

Example programs can be found in the examples folder here.

Creating a connection - solr.Init()

Import the solr package (it is assumed you know how to build/install it, if not, see here) and create a "connection" to your solr server by calling the solr.Init(hostname, port int) function supplying a hostname and port.

// connect to server running on localhost port 8983
s, err := solr.Init("localhost", 8983)

Performing Select Queries - solr.Select()

Select queries are performed using the solr.Select(q *Query) method, passing it a pointer to a Query type.

Here's an example:

q := solr.Query{
    Params: solr.URLParamMap{
        "q": []string{"id:31"},
        "facet.field": []string{"some_field", "some_other_field"},
        "facet": "true",
    },
    Rows: 10,
    Sort: "title ASC",
}

Here we have defined a set of URL parameters - q, facet.field, facet, rows and sort using the solr.Query{} struct. Under the hood this would work out as the following Solr query string:

GET http://localhost:8983/solr/select?q=id:31&facet.field=some_field&facet.field=some_other_field&facet=true

Notice that facet_field, like q, is an array of strings and appears multiple times in the resulting query string (shown above)

Performing a query using our solr.Query() is simple and shown below

res, err := s.Select(&q)
if err != nil {
  fmt.Println(err)
}

// ...

A pointer to q is passed to s.Select(), and returned is a pointer to a SelectResponse (res) and an error (err) if an error occurred.

Iterating over the results is shown later in this document.

Performing 'Raw' Select Queries - solr.SelectRaw()

rsty/solr supports raw queries where you can specify your exact query in string form. This is useful for specifying complex queries where a Query type would be cumbersome. Raw queries are performed as follows:

q := "q={!func}add($v1,$v2)&v1=sqrt(popularity)&v2=100.0" // a solr query
res, err := s.SelectRaw(q)
if err != nil {
    // handle error here
}
// ...

In other words, under the hood the following query will have been performed:

GET http://localhost:8983/solr/select?q={!func}add($v1,$v2)&v1=sqrt(popularity)&v2=100.0

As with solr.Select(), solr.SelectRaw() returns a pointer to a SelectResponse and an error, err.

Responses - SelectResponse type

Responses to select queries (solr.Select() and solr.RawSelect()) come in the form of pointers to SelectResponse types. A SelectResponse wraps a Solr response with a convenient interface. The following few paragraphs and sections describe the various parts of a SelectResponse object

SelectResponse type

A pointer to a SelectResponse and an error are returned from calls to solr.Select() and solr.SelectRaw(). A SelectResponse mimics a Solr response and therefore has the following attributes:

• Results - a pointer to a DocumentCollection (more on this later) which contains the documents returned by Solr
• Status - query status indicator as returned by Solr
• QTime - QTime value as returned by Solr

More information on Status and QTime can be found here.

DocumentCollection object

A DocumentCollection wraps up a set of Documents providing a convenient interface to them.

DocumentCollection supports the following methods:

• Len() int - returns the length (int) of the Documents returned
• Get(i int) *Document - returns a pointer to the document at position i within the Collection

DocumentCollection has the following properties:

• NumFound - the total number of results solr matched to your query (irrespective of the amount returned)
• Facets - an array of Facet objects
• NumFacets - the number of facet fields returned (if any)

Document object

Documents implement the following methods:

• Field(field_name string) interface{} - returns the value of the field, specified by field_name

Faceting

Facet object

If your select query specifies facets, facets will be found under Response.Results.Facets which is an array of Facets. A Facet has the following attributes

• Name - the name of the facet (field) as returned by Solr
• Counts - an array of FacetCounts, the corresponding value counts for the field.

FacetCount object

A FacetCount has the following attributes

• Value - the facet field value
• Count - the count (int) for the field value

Faceting example

Below is an example showing an iteration over a collection of Facets

// q is assumed to have been set up

// perform the query
res, err := s.Query(&q)

// handle error, err, here

results := res.Results
for i := 0; i < results.NumFacets; i++ {
    facet := results.Facets[i]
    fmt.Println("Facet:", facet.Name)
    k := len(facet.Counts)
    for j := 0; j < k; j++ {
        fmt.Println(facet.Counts[j].Value, "=>", facet.Counts[j].Count)
    }
    fmt.Println("")
}

This might output the following:

Facets
------
Facet: category
cameras => 1

Facet: type
digital_slr => 10
compact => 2

Update Queries - solr.Update()

Update queries are used to add, replace or delete documents in Solr's index. Please see the Solr Wiki for more information. Go-Solr uses JSON for update queries, not XML. Solr3.1 will need to be configured to support JSON for update messages, Solr 4.0+ supports JSON natively via /update.

Creating an Update query - example

solr.Update(document map[string]interface{}, commit bool) takes two arguments, an "update document" and a commit flag (boolean) which specifies whether or not a commit should be performed at the same time as the update is performed. An example may look like the following

q, err := solr.Update(document, true);
if err != nil {
    // ...
}

An update document must be of type map[string]interface{}, and may look like the following:

doc := map[string]interface {}{
    "add":[]interface {}{
        map[string]interface {}{"id": 22, "title": "abc"},
        map[string]interface {}{"id": 23, "title": "def"},
        map[string]interface {}{"id": 24, "title": "def"},
    },
}

... which is equivalent to the following JSON:

{"add": [{"id": 22, "title": "abc"}, {"id": 23, "title": "def"}, {"id": 24, "title": "def"}]}

... which is an Update which adds (or replaces) 3 documents in a fictional Solr index.

You can define any type of document to send off to Solr in an update. Support will be added later to allow raw JSON strings to be used in Updates.

solr.Update() returns an UpdateResponse and an error. UpdateResponse has a Success (bool) property.