focal (3) mongoc_database_aggregate.3.gz
NAME
mongoc_database_aggregate - mongoc_database_aggregate()
SYNOPSIS
mongoc_cursor_t *
mongoc_database_aggregate (mongoc_database_t *database,
const bson_t *pipeline,
const bson_t *opts,
const mongoc_read_prefs_t *read_prefs)
BSON_GNUC_WARN_UNUSED_RESULT;
PARAMETERS
• database: A mongoc_database_t.
• pipeline: A bson_t, either a BSON array or a BSON document containing an array field named "pipeline".
• opts: A bson_t containing options for the command, or NULL.
• read_prefs: A mongoc_read_prefs_t or NULL.
opts may be NULL or a BSON document with additional command options:
• readConcern: Construct a mongoc_read_concern_t and use mongoc_read_concern_append to add the read
concern to opts. See the example code for mongoc_client_read_command_with_opts. Read concern requires
MongoDB 3.2 or later, otherwise an error is returned.
• writeConcern: Construct a mongoc_write_concern_t and use mongoc_write_concern_append to add the write
concern to opts. See the example code for mongoc_client_write_command_with_opts.
• sessionId: First, construct a mongoc_client_session_t with mongoc_client_start_session. You can begin a
transaction with mongoc_client_session_start_transaction, optionally with a mongoc_transaction_opt_t
that overrides the options inherited from database, and use mongoc_client_session_append to add the
session to opts. See the example code for mongoc_client_session_t.
• bypassDocumentValidation: Set to true to skip server-side schema validation of the provided BSON
documents.
• collation: Configure textual comparisons. See Setting Collation Order, and the MongoDB Manual entry on
Collation. Collation requires MongoDB 3.2 or later, otherwise an error is returned.
• serverId: To target a specific server, include an int32 "serverId" field. Obtain the id by calling
mongoc_client_select_server, then mongoc_server_description_id on its return value.
• batchSize: An int32 representing number of documents requested to be returned on each call to
mongoc_cursor_next
For a list of all options, see the MongoDB Manual entry on the aggregate command.
DESCRIPTION
This function creates a cursor which sends the aggregate command on the underlying database upon the
first call to mongoc_cursor_next(). For more information on building aggregation pipelines, see the
MongoDB Manual entry on the aggregate command. Note that the pipeline must start with a compatible stage
that does not require an underlying collection (e.g. "$currentOp", "$listLocalSessions").
Read preferences, read and write concern, and collation can be overridden by various sources. The
highest-priority sources for these options are listed first in the following table. In a transaction,
read concern and write concern are prohibited in opts and the read preference must be primary or NULL.
Write concern is applied from opts, or if opts has no write concern and the aggregation pipeline includes
"$out", the write concern is applied from database.
┌─────────────────┬──────────────┬───────────────┬───────────┐
│Read Preferences │ Read Concern │ Write Concern │ Collation │
├─────────────────┼──────────────┼───────────────┼───────────┤
│read_prefs │ opts │ opts │ opts │
├─────────────────┼──────────────┼───────────────┼───────────┤
│Transaction │ Transaction │ Transaction │ │
├─────────────────┼──────────────┼───────────────┼───────────┤
│database │ database │ database │ │
└─────────────────┴──────────────┴───────────────┴───────────┘
See the example for transactions and for the "distinct" command with opts.
This function is considered a retryable read operation unless the pipeline contains a write stage like
$out or $merge. Upon a transient error (a network error, errors due to replica set failover, etc.) the
operation is safely retried once. If retryreads is false in the URI (see mongoc_uri_t) the retry
behavior does not apply.
RETURNS
This function returns a newly allocated mongoc_cursor_t that should be freed with mongoc_cursor_destroy()
when no longer in use. The returned mongoc_cursor_t is never NULL; if the parameters are invalid, the
bson_error_t in the mongoc_cursor_t is filled out, and the mongoc_cursor_t is returned before the server
is selected. The user must call mongoc_cursor_next() on the returned mongoc_cursor_t to execute the
aggregation pipeline.
WARNING:
Failure to handle the result of this function is a programming error.
EXAMPLE
#include <bson/bson.h>
#include <mongoc/mongoc.h>
static mongoc_cursor_t *
current_op_query (mongoc_client_t *client)
{
mongoc_cursor_t *cursor;
mongoc_database_t *database;
bson_t *pipeline;
pipeline = BCON_NEW ("pipeline",
"[",
"{",
"$currentOp",
"{",
"}",
"}",
"]");
/* $currentOp must be run on the admin database */
database = mongoc_client_get_database (client, "admin");
cursor = mongoc_database_aggregate (
database, pipeline, NULL, NULL);
bson_destroy (pipeline);
mongoc_database_destroy (database);
return cursor;
}
AUTHOR
MongoDB, Inc
COPYRIGHT
2017-present, MongoDB, Inc