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How Logi Report Gets Data from MongoDB Databases

Logi Report Designer supports extracting the metadata from the documents of a collection in a MongoDB database, and transforming schemas to relational tables. In the transformation process, elements in a MongoDB collection are transformed to tables according to the ideographic transformation rules, and the hierarchical logic in the MongoDB collection is maintained in the transformed relational schema by joins between the primary key and foreign key in the tables.

This topic includes the following sections:

• Extracting Metadata
• Transforming MongoDB Collections to Relational Schemas

Extracting Metadata

The metadata must be extracted from the documents of a MongoDB collection. The following rules and method for a given document will be applied for the extract.

Extracting rules

• The documents are of the same structure.
• Some elements in the documents can be left blank.
• Documents with different structures will not interrupt the data process.

Extracting method

1. Merge all documents into a single document:

   elementList=new List();

   MergeDocument( Document[] ){

   for each document in Document[]

   for each element in document

   if every E in the elementList does not have the same name as an existing element

   then add the element to elementList.

   }

   If one element in elementList is a document, get all contents of the element in Document[] and merge them.

2. For the merged document, get each element's name, type, and sub type to build an element in the metadata.

Transforming MongoDB Collections to Relational Schemas

When a MongoDB collection is transformed to a relational schema automatically, tables will be built based on the schema.

Transformation rules

Logi Report Designer takes the following rules during the transformation:

• A database is a name space for tables. The tables mapped from a collection in a database belong to this name space.
• A top level document in a collection or an array element which contains documents is mapped to a table.

After a document is mapped to a table, the following elements in the document will be mapped to the columns in the table:

• A simple element in the document or in the embedded document which does not belong to an array.
• An array element that contains a simple element in the document or in the embedded document which does not belong to an array.

However, as MongoDB databases use dynamic collections, a heterogeneous set of documents may be stored within a collection, and only when the data in an array is of the same data type, can it be supported by Logi Report Designer.

Data type conversion rules

Before the data types defined in the MongoDB documents can function with Logi Report Designer, they should be converted into corresponding SQL data types when the MongoDB collections are transformed, following the rules in the tables below.

Sub types for binary

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