Find a document (Go)

Finds a single document in a collection using filter and sort clauses, including vector search.

Ready to write code? See the examples for this method to get started. If you are new to the Data API, check out the quickstart.

Result

Returns a *results.SingleResult pointer to a result object that encapsulates the response and any errors. Call Decode(v any) to unmarshal the document into v. If no document was found, Decode(v any) returns an ErrNoDocuments error.

The fields included in the returned document depend on the subset of fields that were requested in the projection. If requested and applicable, the document will also include a $similarity key with a numeric similarity score that represents the closeness of the sort vector and the document’s vector.

Parameters

Use the FindOne method, which belongs to the Collection type.

Method signature 
func (c *Collection) FindOne(
  ctx context.Context,
  f CollectionFilter,
  opts ...options.CollectionFindOneOption
) *results.SingleResult
Name Type Summary

ctx

context.Context

The context for the operation.

f

CollectionFilter

An object that defines filter criteria using the Data API filter syntax. The method only finds documents that match the filter criteria. Filters can improve performance by reducing the number of documents that the Data API processes.

You must use & to escape any . or & in field names in the filter clause. You cannot use & to escape any other characters. For more information, see Work with . and & in field names (Go).

For a list of available filter operators and more examples, see Filter operators for collections (Go).

Filters can use only indexed fields. If you apply selective indexing when you create a collection, you cannot reference non-indexed fields in a filter.

For an example, see Use filters to find a document.

opts

…​options.CollectionFindOneOption

Optional. A builder to generate options for this operation. See Methods of the options.CollectionFindOneOption builder for more details.
Methods of the options.CollectionFindOneOption builder
Method Summary

SetProjection(v map[string]any)

Optional. Controls which fields are included or excluded in the returned document.

You must use & to escape any . or & in field names in the projection clause. You cannot use & to escape any other characters. For more information, see Work with . and & in field names (Go).

For more information, see Projections for collections (Go).

Default: The default projection for the collection. All fields prefixed with $ are excluded by default and will only be returned if you include them in the projection. _id is included by default and will always be returned unless you exclude it from the projection.

For examples, see Include only specific fields in the response and Exclude specific fields from the response.

SetIncludeSimilarity(v bool)

Optional. Whether to include a $similarity property in the response. The $similarity value represents the closeness of the sort vector and the document’s vector.

This parameter only applies if you use a vector search.

For an example, see Include the similarity score with the result.

Default: False

SetSort(v sort.Sortable)

Optional. Sorts documents by one or more fields, or performs a vector search.

You must use & to escape any . or & in field names in the sort clause. You cannot use & to escape any other characters. For more information, see Work with . and & in field names (Go).

For more information, see Sort clauses for collections (Go).

Sort clauses can use only indexed fields. If you apply selective indexing when you create a collection, you cannot reference non-indexed fields in sort queries.

For vector searches, this parameter can use either $vector or $vectorize.

For examples, see Use sorting to find a document, Use vector search to find a document, and Use vector search and vectorize to find a document.

UpdateAPIOptions(v …​APIOption)

Optional. General API options for this operation, including the timeout.

Examples

The following examples demonstrate how to find a document in a collection.

Use a document’s ID to find a document

All documents have a unique _id property. You can use a filter to find a document with a specific _id.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(ctx, filter.Eq("_id", "101")).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use filters to find a document

You can use a filter to find a document that matches specific criteria. For example, you can find a document with an is_checked_out value of false and a number_of_pages value less than 300.

For a list of available filter operators and more examples, see Filter operators for collections (Go).

Filters can use only indexed fields. If you apply selective indexing when you create a collection, you cannot reference non-indexed fields in a filter.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.And(
			filter.Eq("is_checked_out", false),
			filter.Lt("number_of_pages", 300),
		),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use vector search to find a document

To find the document whose $vector value is most similar to a given vector, use a sort with the vector embeddings that you want to match. For more information, see Find data with vector search.

Vector search is only available for vector-enabled collections. For more information, see Create a collection that can store vector embeddings and $vector in collections (Go).

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		nil,
		options.CollectionFindOne().
			SetSort(sort.Vector([]float32{0.08, -0.62, 0.39})),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use vector search and vectorize to find a document

To find the document whose $vector value is most similar to the $vector value of a given search string, use a sort with the search string that you want to vectorize and match. For more information, see Find data with vector search.

Vector search with vectorize is only available for collections that have vectorize enabled. For more information, see Create a collection that can automatically generate vector embeddings and $vectorize in collections (Go).

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		nil,
		options.CollectionFindOne().
			SetSort(sort.Vectorize("Text to vectorize")),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use lexicographical matching to find a document

Lexicographical matching is currently in public preview. Development is ongoing, and the features and functionality are subject to change. Astra DB Serverless, and the use of such, is subject to the DataStax Preview Terms.

There are two ways to use lexicographical matching to find documents with the Data API:

You can use these strategies together or separately.

You can only use lexicographical matching on collections that have lexical enabled. For more information, see Create a collection that supports lexicographical matching.

Documents must have the $lexical field populated to be included in lexicographical matching. For examples, see Insert a document for retrieval with lexicographical matching and Insert documents for retrieval with lexicographical matching.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.Coll.LexicalMatch("tree hill"),
		options.CollectionFindOne().
			SetSort(sort.Lexical("tree hill grassy")),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use sorting to find a document

You can use a sort clause to sort documents by one or more fields.

For more information, see Sort clauses for collections (Go).

Sort clauses can use only indexed fields. If you apply selective indexing when you create a collection, you cannot reference non-indexed fields in sort queries.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.Eq("metadata.language", "English"),
		options.CollectionFindOne().
			SetSort(sort.Asc("rating").Desc("title")),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Include the similarity score with the result

If you use a vector search to find a document, you can also include a $similarity property in the result. The $similarity value represents the closeness of the sort vector and the document’s vector.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result map[string]any
	err := collection.FindOne(
		ctx,
		filter.F{},
		options.CollectionFindOne().
			SetSort(sort.Vectorize("Text to vectorize")).
			SetIncludeSimilarity(true),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result["$similarity"])
}

Include only specific fields in the response

To specify which fields to include or exclude in the returned document, use a projection.

All fields prefixed with $ are excluded by default and will only be returned if you include them in the projection. _id is included by default and will always be returned unless you exclude it from the projection.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.Eq("metadata.language", "English"),
		options.CollectionFindOne().SetProjection(map[string]any{
			"is_checked_out": true,
			"title":          true,
		}),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Exclude specific fields from the response

To specify which fields to include or exclude in the returned document, use a projection.

All fields prefixed with $ are excluded by default and will only be returned if you include them in the projection. _id is included by default and will always be returned unless you exclude it from the projection.

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.Eq("metadata.language", "English"),
		options.CollectionFindOne().SetProjection(map[string]any{
			"is_checked_out": false,
			"title":          false,
		}),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Use filter, sort, and projection together

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.And(
			filter.Eq("is_checked_out", false),
			filter.Lt("number_of_pages", 300),
		),
		options.CollectionFindOne().
			SetSort(sort.Asc("rating").Desc("title")).
			SetProjection(map[string]any{"is_checked_out": true, "title": true}),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Work with . and & in field names

You must use & to escape any . or & in field names when the field is used in a filter, sort, projection, update, or indexing clause. Dot notation, which is used to reference nested fields, should not be escaped. For more information, see Work with . and & in field names (Go).

For example, in the following document, you would use escaping like this: areas.r&&d, costs.price&.usd, and costs.price&.cad.

{
  "areas": {
    "r&d": true,
    "design": false
  },
  "costs": {
    "price.usd": 100,
    "price.cad": 90
  }
}
package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.And(
			filter.Eq("areas.r&&d", false),
			filter.Lt("costs.price&.usd", 300),
		),
		options.CollectionFindOne().
			SetSort(sort.Asc("costs.price&.usd")).
			SetProjection(map[string]any{
				"areas.r&&d":       true,
				"costs.price&.cad": true,
			}),
	).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

You can also use the EscapeFieldNames function provided by the client:

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/datastax/astra-db-go/v2/astra"
	"github.com/datastax/astra-db-go/v2/astra/filter"
	"github.com/datastax/astra-db-go/v2/astra/options"
	"github.com/datastax/astra-db-go/v2/astra/sort"
)

func main() {
	ctx := context.Background()

	// Get an existing collection
	client := astra.NewClient()

	database := client.Database(
		"API_ENDPOINT",
		options.API().SetToken("APPLICATION_TOKEN"),
	)

	collection := database.Collection("COLLECTION_NAME")

	// Find a document
	var result astra.Document
	err := collection.FindOne(
		ctx,
		filter.And(
			filter.Eq(astra.EscapeFieldNames("areas", "r&d"), false),
			filter.Lt(astra.EscapeFieldNames("costs", "price.usd"), 300),
		),
		options.CollectionFindOne().
			SetSort(sort.Asc(astra.EscapeFieldNames("costs", "price.usd"))).
			SetProjection(map[string]any{
				astra.EscapeFieldNames("areas", "r&d"):       true,
				astra.EscapeFieldNames("costs", "price.cad"): true,
			})).Decode(&result)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(result.ToMap())
}

Client reference

For more information, see the client reference.

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