Querying Data in Apache Solr

Apache Solr provides the facility of querying data, too, in addition to storing data. Solr gives a certain parameters using which users can query the stored data in it.

In the below-given table, we have listed down the various query parameters available in Apache Solr.

We can see all the above parameters as options to query Solr documents. Go to the homepage of Apache Solr, and on the left-hand side of the page, click on the Query. We will be redirected to the fields for the parameters of a query.

Retrieving the Records

Let's suppose we have three different records in the core named as my_core. To get detailed data from the selected core, we have to pass the name-value pairs of the fields for the soecified document. E.g, if we want to get the record with the value of the field id, we have to pass the name and value pair of the field as - Id:001 as value for the q parameter and run the query command.

Similarly, we can fetch all the records from an index by passing *:* as a value to the q, as displayed in the below-given screenshot.

We can get the records from the secondary record by passing two as a value to the start parameter, as displayed in the below-given screenshot.

Restricting the Number of Records

We can restrict the quantity of records by defining a value in the parameter rows. E.g., we can restrict the total number of records in the Query to 2, bypassing the value two into the parameter rows, as displayed in the given screenshot below.

Response Writer Type

We can fetch the required document type response by choosing one from the provided data of the wt parameter.

We have selected the .csv format to get the response from the Apache Solr in the above image.

List of the Fields

In case we want particular fields in the output documents, we need to pass the list of the required fields, separated by commas, as a value to the property fl.

In the example below, we retrieving the fields - id, phone, and first_name.

Spell-check

We'll see to use Solr's spell-check search component. Automated spell-checking is a core search feature that most users expect to work without having to think. When it comes to spell-checking, there are four general scenarios you need to consider:

• The Query shown contains one or more misspelled terms leading to no relevant hits. if a suggestion is available, our search client should auto-execute the suggested term and show the user an informational message. For example, we Searched for atmosphere instead of the atmosphere.
• It contains a rare term resulting in a few hits; suggestions are available and have more hits, so you may want to prompt the user with did you mean …?
• It contains a correctly spelled term, but they have fewer or about the same data as provided in the query term. Our search solution should not prompt the user with an alternate decision.
• The Query contains a term that does not exist in your index; suggestions are not available.

From the above given scenarios, we can get two key requirements of a spell-checking solution:

• We need to identify suggested terms for each term in our Query, i.e., some dictionary to look up terms that are similar to terms entered by users.
• Second, we need to know how many documents all the suggested term matches.

Spell-check example

We can use the http command-line utility for running code listings to query Apache Solr with the misspelled term atmosphere, as seen in this listing.

Query Solr with a misspelled query term "atmosphear."

Query

Response