tMongoDBGridFSGet Standard properties

Property type

Either Built-In or Repository.

Built-In: No property data stored centrally.

Repository: Select the repository file where the properties are stored.

Use an existing connection

Select this check box and in the Component List drop-down list, select the desired connection component to reuse the connection details you already defined.

Note that when a Job contains the parent Job and the child Job, Component List presents only the connection components in the same Job level.

Use replica set address or multiple query routers

Select this check box to show the Server addresses table.

In the Server addresses table, define the sharded MongoDB databases or the MongoDB replica sets you want to connect to.

Server and Port

IP address and listening port of the database server.

Available when the Use replica set address check box is not selected.

Note that if you use the authentication mechanisms to connect to this MongoDB database, you must enter the name, rather than the IP address, of the host of the database server.

Database

Name of the database.

Use SSL connection

Select this check box to enable the SSL or TLS encrypted connection.

Then you need to use the tSetKeystore component in the same Job to specify the encryption information.

Note that the SSL connection is available only for the version 2.4 + of MongoDB.

Set read preference

Select this check box and from the Read preference drop-down list that is displayed, select the member to which you need to direct the read operations.

If you leave this check box clear, the Job uses the default Read preference, that is to say, uses the primary member in a replica set.

For further information, see MongoDB's documentation about Replication and its Read preferences.

Required authentication

Select this check box to enable the database authentication.

Among the mechanisms listed on the Authentication mechanism drop-down list, the NEGOTIATE one is recommended if you are not using Kerberos, because it automatically select the authentication mechanism the most adapted to the MongoDB version you are using.

For details about the other mechanisms in this list, see MongoDB Authentication from the MongoDB documentation.

Set Authentication database

If the username to be used to connect to MongoDB has been created in a specific Authentication database of MongoDB, select this check box to enter the name of this Authentication database in the Authentication database field that is displayed.

For further information about the MongoDB Authentication database, see User Authentication database.

Username and Password

DB user authentication data.

To enter the password, click the [...] button next to the password field, and then in the pop-up dialog box enter the password between double quotes and click OK to save the settings.

Available when the Required authentication check box is selected.

If the security system you have selected from the Authentication mechanism drop-down list is Kerberos, you need to enter the User principal, the Realm and the KDC server fields instead of the Username and the Password fields.

Bucket

Enter the name of the bucket you need to read files from. A bucket of GridFS is similar to a folder.

Query type

Select the type of the query you want tMongoDBGridFSGet to perform to select the data to be copied.

• Filename: you need to enter the name of the file to be copied. This name is the value of the filename attribute used by this file. Note that only one name is allowed.

  In GridFS, a file is identified only by its unique identifier (its object ID); its file name is not necessarily unique.

• Mongo Query: enter the query to be used to select the files to be copied.

  The default query, {} within double quotation marks provided with this component, means to select all of the files. You can also apply a regular expression by putting {'filename':{'$regex':'REGEX_PATTERN'}} to define the file names to be used.

It is recommended to use your query along with the Overwrite local files and the Use Document ID as output filename check boxes to avoid any file name conflict issue.

Local Folder

Enter the path to the folder in which the data copied from GridFS is to be written.

Overwrite local files

Select this check box to overwrite the file using the same file name in the local folder being used. Otherwise, an exception will be returned in this type of situation.

Use Document ID as output filename

Select this box to rename the incoming files on the fly using the values of their object IDs. This allows you keep the files that have the same file names.

tStatCatcher Statistics

Select this check box to collect the log data at the component level.

No query timeout

Select this check box to prevent MongoDB servers from stopping idle cursors at the end of 10-minute inactivity of these cursors. In this situation, an idle cursor will stay open until either the results of this cursor are exhausted or you manually close it using the cursor.close() method.

A cursor for MongoDB is a pointer to the result set of a query. By default, that is to say, with this check box being clear, a MongoDB server automatically stops idle cursors after a given inactivity period to avoid excess memory use. For further information about MongoDB cursors, see https://docs.mongodb.org/manual/core/cursors/.

Global Variables

NB_FILE: the number of files processed. This is an After variable and it returns an integer.

ERROR_MESSAGE: the error message generated by the component when an error occurs. This is an After variable and it returns a string. This variable functions only if the Die on error check box is cleared, if the component has this check box.

A Flow variable functions during the execution of a component while an After variable functions after the execution of the component.

To fill up a field or expression with a variable, press Ctrl + Space to access the variable list and choose the variable to use from it.

For further information about variables, see Talend Studio User Guide.

Usage rule

This component combines MongoDB GridFS connection and data extraction, thus usually used as a single-component subJob to copy data from GridFS to a user-defined local directory.

It is often connected to the Job using OnSubjobOk or OnComponentOk link, depending on the context.