There are two ways to access metadata with dotConnect for MongoDB: using the GetSchema method of MongoDBConnection or querying the information schema tables, described in the Information Schema topic. This topic describes the GetSchema method.

dotConnect for MongoDB provides the GetSchema method of MongoDBConnection for getting MongoDB metadata. The method is defined by the System.Data.Common.DbConnection class and follows the standard ADO.NET GetSchema API. It allows you to read server schema information without writing queries and parsing the output. You can get information about databases (catalogs), collections (tables), fields (columns), indexes, and keys. MongoDB has no foreign keys, so there are no metadata collections for them.

This article consists of the following sections:

• How To Use
• GetSchema Method Reference
• GetSchema Resultset Columns
• Samples

How To Use

The GetSchema method has three overloads. All overloads return a System.Data.DataTable object that contains information about server elements.

public virtual DataTable GetSchema();

If you call the GetSchema method without parameters, or with the single parameter "MetaDataCollections" (which is the same), the returned table contains the list of all metadata collections. The first column of each row is a collection name that you can pass to the method as the collectionName argument. The second column is the number of restriction values for this collection.

public virtual DataTable GetSchema(
   string collectionName
);

GetSchema with one argument returns general information about the specified metadata collection. For example, GetSchema("Tables") returns the list of the collections of the MongoDB server.

public virtual DataTable GetSchema(
   string collectionName,
   string[] restrictionValues
);

In this overload, the first parameter is the name of a metadata collection, and the second parameter is the array of restrictions to apply when querying information. The restrictions specify which subset of the collection to return, for example, only the collections of a certain database. The number and description of the restrictions allowed for each metadata collection are provided in the table below. Their number can also be obtained from the result of the GetSchema() method. If the second parameter is null, it is ignored. A restriction with a null value matches all values; for example, if the database restriction is null, the metadata of all databases of the server is returned. In the Catalogs collection (CatalogName), in the Tables collection (TableName), and in the Columns collection (ColumnName), a restriction can contain the wildcards '%' (any number of characters) and '_' (one character).

Instead of specifying the metadata collection name as a string constant, you can use the members of System.Data.DbMetaDataCollectionNames as the first argument of the GetSchema method. The members of this class are string constants that correspond to the names of the metadata collections.

GetSchema Method Reference

The following table provides detailed information on the metadata collections that can be retrieved using the GetSchema method, and the restrictions that can be applied to them. When calling the GetSchema method, you can pass all or some of the restrictions. A restriction that you do not specify, or specify as null, matches all values.

GetSchema Resultset Columns

For each metadata collection, dotConnect for MongoDB returns a DataTable with its own set of columns.

Columns

For the Columns collection, the result DataTable contains the following columns:

Tables

For the Tables collection, the result DataTable contains the following columns:

MetaDataCollections

For the MetaDataCollections collection, the result DataTable contains the following columns:

ReservedWords

For the ReservedWords collection, the result DataTable contains the following column:

DataSourceInformation and DataTypes

The DataSourceInformation and DataTypes collections return the standard columns of these metadata collections of ADO.NET.

Restrictions

For the Restrictions collection, the result DataTable contains the following columns:

Catalogs

For the Catalogs collection, the result DataTable contains the following column:

Indexes, PrimaryKeys, and UniqueKeys

For the Indexes, PrimaryKeys, and UniqueKeys collections, the result DataTable contains the following columns:

For PrimaryKeys and UniqueKeys, the restriction with the name of the index is called KeyName, but the result column with the name of the index is IndexName in all three collections.

IndexColumns

For the IndexColumns collection, the result DataTable contains the following columns:

Samples

The following example returns the columns of the customers collection of the sample database. The first restriction of the Columns collection is the database. If it is null, the columns of all databases of the server are returned, so the database is specified explicitly in this example.

using (var connection = new MongoDBConnection("Host=localhost;Database=sample;User Id=user;Password=pwd;License Key=***")) {
  connection.Open();
  DataTable columns = connection.GetSchema("Columns", new string[] { "sample", "customers" });
  foreach (DataRow row in columns.Rows)
    Console.WriteLine("{0}\t{1}", row["ColumnName"], row["DataType"]);
}

For documents of the { name, address: { city, street } } structure, the example outputs the following:

_id             System.String
name            System.String
address.city    System.String
address.street  System.String

The following example lists the databases of the server.

DataTable catalogs = connection.GetSchema("Catalogs");
foreach (DataRow row in catalogs.Rows)
    Console.WriteLine(row["CatalogName"]);

The following example lists the collections of the sample database. The first restriction of the Tables collection is the database name.

DataTable tables = connection.GetSchema("Tables", new string[] { "sample" });
foreach (DataRow row in tables.Rows)
    Console.WriteLine("{0} ({1})", row["TableName"], row["TableType"]);

The following example retrieves the indexes of the customers collection. The restrictions are the database name and the collection name; a null value for a restriction matches all values.

DataTable indexes = connection.GetSchema("Indexes", new string[] { "sample", "customers" });
foreach (DataRow row in indexes.Rows)
    Console.WriteLine("{0}: Unique={1}", row["IndexName"], row["IsUnique"]);

See Also

Metadata | Metadata Overview | Information Schema