dotConnect for Salesforce provides two ways of getting Salesforce.com or Database.com metadata: GetSchema method and metadata tables, compliant with the SQL-92 information schema standard.
GetSchema method allows you to read server schema information without writing queries and parsing the output. All information you may want to obtain is brought to you by single function in easy-to-process format. You can get information on tables, columns, and constraints. The method is introduced in System.Data.Common.DbConnection.
This article consists of the following sections:
GetSchema method is available in three overloads, each of them serves its own purpose. All overloads return System.Data.DataTable object that contains information about server elements.
If you call the GetSchema method without parameters, or with single parameter "MetaDataCollections" (which is actually the same), the table object returned by the method will contain three columns. The first field of every row is a keyword allowed to be passed to the method (as collectionName argument). The second field is the number of restriction values for this keywords (passed through restrictionValues argument). The third field is not used in dotConnect for Salesforce. It is always zero.
GetSchema with 1 argument returns general information about the collection queried. For example, GetSchema("Tables") returns the list of the tables (objects) in your Salesforce.com or Database.com account.
In this overload first parameter is name of a collection, and second parameter is the array of restrictions to be applied when querying information. These restrictions specify which subset of the collection will be returned. The restrictions can include, for example, the table name (in this case, only collection elements belonging to this table will be returned). The quantity and description of restrictions allowed for each metadata collection are represented in the table here. Their number can also be obtained from the return of the GetSchema() method. If the second parameter is null/Nothing, it is ignored.
Instead of specifying the metadata collection name as a string constant, you may use members of System.Data.DbMetaDataCollectionNames and Devart.Data.Salesforce.SalesforceMetadataCollectionNames as the first GetSchema argument values. The members of these classes are the string fields, each field stores the corresponding metadata collection name. It is recommended to use these fields rather than manually input the collection names manually as the string constants because in case of using these fields, you will find misspellings at compile-time, and intellisense will show you all the available metadata collection names.
The following table provides detailed information on metadata collections that can be retrieved using the GetSchema method, and restrictions that can be applied for them. When calling the GetSchema method, you can pass all or few arguments. In the latter case, some default values are assumed, if they were not specified explicitly.
Collection Name |
Number of restrictions | Return value |
Restriction descriptions |
---|---|---|---|
Columns | 2 |
Returns list of columns, their type and some extra information. |
|
DataSourceInformation | 0 |
Returns information about the data source. |
|
DataTypes | 0 |
Returns information about data types supported by the data source. |
|
ForeignKeyColumns | 3 |
Returns list of columns used by foreign keys. |
|
ForeignKeys | 3 |
Returns list of columns that participate in foreign keys. |
|
IndexColumns | 2 |
Returns list of columns that participate in indexes. |
|
Indexes | 2 |
Returns list of columns that participate in indexes. |
|
MetaDataCollections | 0 |
Returns this list. Same as using GetSchema() method without parameters. |
|
PrimaryKeyColumns | 2 |
Returns list of columns used by primary keys. |
|
PrimaryKeys | 2 |
Returns list of columns that participate in primary keys. |
|
ReservedWords | 0 |
Lists all reserved words used in the server. |
|
Restrictions | 0 |
Returns list of possible restrictions and their default values for the metadata collections. |
|
Tables | 1 |
GetSchema("Tables") returns the list of the account tables (objects). |
|
UniqueKeyColumns | 2 |
Returns list of columns that participate in unique keys. |
|
UniqueKeys | 1 |
Returns list of unique keys of the specified tables. |
|
The following code fragment is an elegant way to detect existence of a table.
The next sample shows how to retrieve columns information from a table and render it to console.
>Also you can get a metadata of query result set using the GetSchemaTable method of SalesforceDataReader.
Metadata | Metadata Overview | Information Schema | SalesforceConnection Class | DbConnectionBase.GetSchema Method