# Search

OpenSearch provides a powerful search API that allows you to search for documents in an index. The search API supports a number of parameters that allow you to customize the search operation. In this guide, we will explore the search API and its parameters.

# Setup

Let's start by creating an index and adding some documents to it:

```rust
let url = Url::parse("https://localhost:9200")?;
let credentials = Credentials::Basic("admin".into(), "admin".into());
let transport = TransportBuilder::new(SingleNodeConnectionPool::new(url))
    .cert_validation(CertificateValidation::None)
    .auth(credentials)
    .build()?;
let client = OpenSearch::new(transport);
client
  .indices()
  .create(IndicesCreateParts::Index("movies"))
  .send()
  .await?;

for i in 0..11 {
    client
        .index(IndexParts::IndexId("movies", &i.to_string()))
        .body(json!({
            "title": format!("The Dark Knight {}", i),
            "director": "Christopher Nolan",
            "year": 2008 + i
        }))
        .send()
        .await?;
}

client
    .index(IndexParts::Index("movies"))
    .body(json!({
        "title": "The Godfather",
        "director": "Francis Ford Coppola",
        "year": "1972"
    }))
    .send()
    .await?;

client
    .index(IndexParts::Index("movies"))
    .body(json!({
        "title": "The Shawshank Redemption",
        "director": "Frank Darabont",
        "year": "1994"
    }))
    .send()
    .await?;

// Refresh the index to make the documents searchable
client
    .indices()
    .refresh(IndicesRefreshParts::Index(&["movies"]))
    .send()
    .await?;
```

## Search API

### Basic Search

The search API allows you to search for documents in an index. The following example searches for ALL documents in the `movies` index:

```rust
let response = client
    .search(SearchParts::Index(&["movies"]))
    .send()
    .await?
    .json::<Value>()
    .await?;
println!("{}", response["hits"]["count"]);
```

You can also search for documents that match a specific query. The following example searches for documents that match the query `dark knight`:

```rust
let response = client
    .search(SearchParts::Index(&["movies"]))
    .body(json!({
        "query": {
            "multi_match": {
                "query": "dark knight",
                "fields": ["title"]
            }
        }
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
println!("{:?}", response["hits"]["hits"].as_array().unwrap());
```

OpenSearch query DSL allows you to specify complex queries. Check out the [OpenSearch query DSL documentation](https://opensearch.org/docs/latest/query-dsl/) for more information.

### Basic Pagination

The search API allows you to paginate through the search results. The following example searches for documents that match the query `dark knight`, sorted by `year` in ascending order, and returns the first 2 results after skipping the first 5 results:

```rust
let response = client
    .search(SearchParts::Index(&["movies"]))
    .from(5)
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
println!("{:?}", response["hits"]["hits"].as_array().unwrap());
```

With sorting, you can also use the `search_after` parameter to paginate through the search results. Let's say you have already displayed the first page of results, and you want to display the next page. You can use the `search_after` parameter to paginate through the search results. The following example will demonstrate how to get the first 3 pages of results using the search query of the previous example:

```rust
let page_1 = client
    .search(SearchParts::Index(&["movies"]))
    .from(5)
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_1_hits = page_1["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_1_hits);

let page_2 = client
    .search(SearchParts::Index(&["movies"]))
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ],
        "search_after": page_1_hits[page_1_hits.len() - 1]["sort"]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_2_hits = page_2["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_2_hits);

let page_3 = client
    .search(SearchParts::Index(&["movies"]))
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ],
        "search_after": page_2_hits[page_2_hits.len() - 1]["sort"]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_3_hits = page_3["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_3_hits);
```

### Pagination with scroll

When retrieving large amounts of non-real-time data, you can use the `scroll` parameter to paginate through the search results.

```rust
let page_1 = client
    .search(SearchParts::Index(&["movies"]))
    .scroll("1m")
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;

let page_2 = client
    .scroll(ScrollParts::None)
    .scroll_id(page_1["_scroll_id"].as_str().unwrap())
    .scroll("1m")
    .send()
    .await?
    .json::<Value>()
    .await?;

let page_3 = client
    .scroll(ScrollParts::None)
    .scroll_id(page_2["_scroll_id"].as_str().unwrap())
    .scroll("1m")
    .send()
    .await?
    .json::<Value>()
    .await?;
```

### Pagination with Point in Time

The scroll example above has one weakness: if the index is updated while you are scrolling through the results, they will be paginated inconsistently. To avoid this, you should use the "Point in Time" feature. The following example demonstrates how to use the point_in_time and pit_id parameters to paginate through the search results:

```rust
// Create a point in time
let pit_id = client
    .create_pit(CreatePitParts::Index(&["movies"]))
    .keep_alive("1m")
    .send()
    .await?
    .json::<Value>()
    .await?["pit_id"]
    .to_string();

// Get the first 3 pages of results, including pit info in the search body
let page_1 = client
    .search(SearchParts::None)
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ],
        "pit": {
            "id": pit_id,
            "keep_alive": "1m"
        }
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_1_hits = page_1["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_1_hits);

let page_2 = client
    .search(SearchParts::None)
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ],
        "pit": {
            "id": pit_id,
            "keep_alive": "1m"
        },
        "search_after": page_1_hits[page_1_hits.len() - 1]["sort"]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_2_hits = page_2["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_2_hits);

let page_3 = client
    .search(SearchParts::None)
    .size(2)
    .body(json!({
        "query": {
            "match": {
                "title": "dark knight"
            }
        },
        "sort": [
            {
                "year": {
                    "order": "asc"
                }
            }
        ],
        "pit": {
            "id": pit_id,
            "keep_alive": "1m"
        },
        "search_after": page_2_hits[page_2_hits.len() - 1]["sort"]
    }))
    .send()
    .await?
    .json::<Value>()
    .await?;
let page_3_hits = page_3["hits"]["hits"].as_array().unwrap();
println!("{:?}", page_3_hits);

// Print out the titles of the first 3 pages of results
page_1_hits
    .iter()
    .for_each(|hit| println!("{}", hit["_source"]["title"]));
page_2_hits
    .iter()
    .for_each(|hit| println!("{}", hit["_source"]["title"]));
page_3_hits
    .iter()
    .for_each(|hit| println!("{}", hit["_source"]["title"]));

// Delete the point in time
client
    .delete_pit()
    .body(json!({ "pit_id": pit_id }))
    .send()
    .await?;
```

Note that a point-in-time is associated with an index or a set of index. So, when performing a search with a point-in-time, you DO NOT specify the index in the search.

## Cleanup

```rust
client
    .indices()
    .delete(IndicesDeleteParts::Index(&["movies"]))
    .send()
    .await?;
```