MongoDBReader

Home \| Table of Contents	MongoDBReader	CloverETL 4.6.1
Prev	Readers	Next

Short Description

MongoDBReader reads data from the MongoDB™ database using the Java driver. ^[1]

MongoDBReader reads data from the MongoDB database using the find database command. It can also perform the aggregate, count and distinct commands.

Component	Data source	Input ports	Output ports	Each to all outputs	Different to different outputs	Transformation	Transf. req.	Java	CTL	Auto-propagated metadata
MongoDBReader	database	0-1	1-2

Icon

Ports

Port type	Number	Description	Metadata
Input	0	Input data records to be mapped to component attributes.	any
Output	0	Results	any
Output	1	Errors	any

Metadata

MongoDBReader does not propagate metadata.

This component has metadata templates available. See details on Metadata Templates.

Input

Table 48.8. MongoDBReader_Attributes

Field number	Field name	Data type
1	collection	string
2	query	string
3	projection	string
4	orderBy	string
5	skip	integer
6	limit	integer

Output

Table 48.9. MongoDBReader_Result

Field number	Field name	Data type
1	stringValue	string
2	jsonObject	[string,string]
3	count	long

Error

Table 48.10. MongoDBReader_Error

Field number	Field name	Data type	Description
1	errorMessage	string
2	stackTrace	string

MongoDBReader Attributes

Attribute	Req	Description	Possible values
Basic
Connection		ID of the MongoDB connection to be used.
Collection name	^{[ 1]}	The name of the source collection.
Operation		The operation to be performed.	find (default) \| aggregate \| count \| distinct
Query		A query that selects only matching documents from a collection. The selection criteria may contain query operators. To return all documents in a collection, omit this parameter. For the `aggregate` operation, the attribute specifies the aggregation pipeline operators as a comma-separated list.	BSON document \| comma-separated list of BSON documents (`aggregate` only)
Projection		Specifies the fields to return using projection operators: `{ field1: boolean, field2: boolean ... }` The boolean can take the following include or exclude values: `1` or `true` to include. The `_id` field is included by default, unless explicitly excluded. `0` or `false` to exclude. The Projection cannot contain both include and exclude specifications except for the exclusion of the `_id` field. To return all fields in the matching document, omit this parameter. For the `distinct` operation, the attribute is required and specifies the name of the field to collect distinct values from.	BSON document \| field name (`distinct` only)
Order by		Sorts the result of the `find` operation. For each field in the Order by document, if the field's corresponding value is positive, then the query results will be sorted in ascending order for that attribute; if the field's corresponding value is negative, then the results will be sorted in descending order. The attribute affects only the `find` operation.	BSON document
Skip		Set the starting point of a result of the `find` operation by skipping the first `N` documents. The attribute affects only the `find` operation.
Limit		Specifies the maximum number of documents the `find` operation will return. The attribute affects only the `find` operation.
Input mapping	^{[ 2]}	Defines mapping of input records to component attributes.
Output mapping		Defines mapping of results to standard output port.
Error mapping	^{[ 2]}	Defines mapping of errors to error output port.
Advanced
Query options		Specifies the query options for the `find` operation. See `com.mongodb.Bytes.QUERYOPTION_*` for the list of available options. The attribute is ignored by all operations other than `find`.
Field pattern		Specifies the format of placeholders that can be used within the Query, Projection and Order by attributes. The value of the attribute must contain "`field`" as a substring, e.g. "`<field>`", "`#{field}`", etc. During the execution, each placeholder is replaced using simple string substitution with the value of the respective input field, e.g. the string "`@{name}`" will be replaced with the value of the input field called "`name`" (assuming the default format of the placeholders).	@{field} (default) \| any string containing "`field`" as a substring
^{[ 1]}The attribute is required, unless specified in the Input mapping. ^{[ 2]}Required if the corresponding edge is connected.

Details

By default, MongoDBReader performs the find() operation.

It can also be used to execute the aggregate(), count() or distinct() operations.

The result set elements can be mapped one by one to the first output port using the Output mapping attribute.

Editing any of the Input, Output or Error mapping opens the Transform Editor.

Input mapping

The editor allows you to override selected attributes of the component with the values of the input fields.

Field Name	Attribute	Type
collection	Collection	string
query	Query	string
projection	Projection	string
orderBy	Order by	string
skip	Skip	integer
limit	Limit	integer

Output mapping

The editor allows you to map the results and the input data to the output port.

If output mapping is empty, fields of input record and result record are mapped to output by name.

Field Name	Type	Description
stringValue	string	Contains the current element of the result set converted to a string.
jsonObject	map[string, string]	Conditional. Contains the current result set element, if it is a JSON object. The values of the object are serialized to strings.
count	long	Only used for the count operation, contains the number of matching documents.

Error mapping

The editor allows you to map the errors and the input data to the error port.

If error mapping is empty, fields of input record and result record are mapped to output by name.

Field Name	Type	Description
errorMessage	string	The error message.
stackTrace	string	The stack trace of the error.

In queries you can use extended JSON, e.g. {_id: {$oid: "53b0e84b72a0ec06118b45fd"}} Similar format is used for passing long data type, timestamp, binary data etc. See http://docs.mongodb.org/manual/reference/mongodb-extended-json/

Examples

Let us assume that the documents in the source collection resemble the following:

{
	customer : "John",
	value : 123
}

Executing a Query

If executed without any parameter, the find operation will list all the documents in the source collection.

If the Query attribute is set to { customer: { $in: [ "John", "Jane" ] } }, the result set will only contain documents whose "customer" field has the value "John" or "Jane".
If the Projection attribute is set to { customer: 1 }, the result set will only contain the "_id" and "customer" fields.
If the Order by attribute is set to { value: 1 }, the result set will be sorted by the "value" field in ascending order.
If the Skip attribute is set to 5, the first five documents in the result set will be skipped.
If the Limit attribute is set to 20, at most 20 documents will be returned.

Aggregation

Consider the following aggregation pipeline:

{ $group : { _id : "$customer", sum : { $sum : "$value" } } }, 
{ $match : { sum : { $gt : 1500 } } },
{ $sort : { sum : -1 } },
{ $limit : 10 },
{ $project : { _id : 0, name : { $toUpper : "$_id" }, total : "$sum" } }

The first line groups documents by the "customer" field and computes the sum of the respective "value" fields.
The second line filters the aggregated values and selects only those having the sum greater than 1500.
The third line sorts the results by the sum in descending order.
The fourth line limits the number of results to 10.
The last line renames the fields and converts the names to upper case.

Count

The count operation can be limited to documents matching the specified Query. For example, { value : { $gt : 150 } } will count the number of documents whose "value" field has a value greater than 150.

The result is returned as the count output field.

Distinct Values

We could use the distinct operation to retrieve the list of names of all the customers - set the value of the Projection attribute to customer (without quotes). Optionally, a Query may be specified to limit the input documents for the distinct analysis.

Reading Object with Specific ID

You can query for an object having the specific object ID.

{ _id: {"$oid" : "54ca707ceac6b571fb4aa285"}}