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| Querying the Metadata Container |
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Programmer's Guide > Feature Reference > API > OpenAccess Metadata > Metadata Container > Querying the Metadata Container |
The purpose of this tutorial is to show you how to execute LINQ queries against the MetadataContainer, and to collect statistics about your domain model.
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All examples in this article will use the entities of the Northwind database. |
Example 1: Persistent Types
The following example shows a LINQ to Objects query which queries the metadata model and displays all the entity names.
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var query = from meta in container.PersistentTypes
select new
{
meta.Name,
meta.Namespace,
meta.IdentityType,
meta.IsArtificial,
meta.DataAccessKind
}; |
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Dim query = From meta In container.PersistentTypes
Select New With {Key meta.Name, Key meta.Namespace, Key meta.IdentityType, Key meta.IsArtificial, Key meta.DataAccessKind} |
Example 2: Tables
Similarly to the previous example you could extract information about the tables in your database.
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var query = from meta in container.Tables
select new
{
meta.Name,
meta.PKConstraintName
}; |
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Dim query = From meta In container.Tables
Select New With {Key meta.Name, Key meta.PKConstraintName} |
Example 3: Inherited Persistent Types
You can also check inheritance and query the PersistentTypes which are derived from a base class.
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var query = from meta in container.PersistentTypes
select new
{
meta.Name,
BaseTypeName = meta.BaseType != null ? meta.BaseType.Name : null
}; |
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Dim query = From meta In container.PersistentTypes
Select New With {Key meta.Name, Key .BaseTypeName = If(meta.BaseType IsNot Nothing, meta.BaseType.Name, Nothing)} |
Example 4: Persistent Types and Properties
The following query will aggregate all properties and some of their characteristics like DefaultValue and Description.
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var query = from meta in container.PersistentTypes
let members = meta.Members
select new
{
EntityName = meta.Name,
MembersCount = members.Count,
MemberNames = from p in members
select new
{
p.Name,
p.IsArtificial,
p.Description,
p.DataAccessKind
}
}; |
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Dim query = From meta In container.PersistentTypes
Let members = meta.Members
Select New With {Key .EntityName = meta.Name, Key .MembersCount = members.Count, Key .MemberNames =
From p In members
Select New With {Key p.Name, Key p.IsArtificial, Key p.Description, Key p.DataAccessKind}} |
Example 5: Properties
The following example is absolutely the same as the previous example, however it flattens the result.
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var query = from meta in container.PersistentTypes
from p in meta.Members
select new
{
EntityName = meta.Name,
MembersCount = meta.Members.Count,
FieldName = p.Name,
IsArtificial = p.IsArtificial,
Description = p.Description,
DataAccessKind = p.DataAccessKind,
MemberType = p.MemberType != null ? p.MemberType.Name : null
}; |
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Dim query = From meta In container.PersistentTypes , p In meta.Members
Select New With {Key .EntityName = meta.Name, Key .MembersCount = meta.Members.Count, Key .FieldName = p.Name, Key .IsArtificial = p.IsArtificial, Key .Description = p.Description, Key .DataAccessKind = p.DataAccessKind, Key .MemberType = If(p.MemberType IsNot Nothing, p.MemberType.Name, Nothing)} |
Example 6: Properties
Now you have a simple collection with all the info about the properties. It is quite easy to query this collection again and to get all string properties that are not nullable.
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var properties = from meta in container.PersistentTypes
from p in meta.Members
select new
{
EntityName = meta.Name,
MembersCount = meta.Members.Count,
FieldName = p.Name,
IsArtificial = p.IsArtificial,
Description = p.Description,
DataAccessKind = p.DataAccessKind,
MemberType = p.MemberType
};
var query = from p in properties
where p.MemberType != null && p.MemberType.ToString() == "String"
select p; |
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Dim properties = From meta In container.PersistentTypes , p In meta.Members
Select New With {Key .EntityName = meta.Name, Key .MembersCount = meta.Members.Count, Key .FieldName = p.Name, Key .IsArtificial = p.IsArtificial, Key .Description = p.Description, Key .DataAccessKind = p.DataAccessKind, Key .MemberType = p.MemberType}
Dim query = From p In properties
Where p.MemberType IsNot Nothing AndAlso p.MemberType.ToString() = "String"
Select p |
Example 7: Properties
This data can also be used to create statistics. The following example will show how many properties of each (primitive) type are defined in your metadata model.
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var properties = from meta in container.PersistentTypes
from p in meta.Members
select new
{
EntityName = meta.Name,
MembersCount = meta.Members.Count,
FieldName = p.Name,
IsArtificial = p.IsArtificial,
Description = p.Description,
DataAccessKind = p.DataAccessKind,
MemberType = p.MemberType != null ? p.MemberType.Name : null
};
var query = (from p in properties
group p by p.MemberType into gr
select new
{
Type = gr.Key,
Count = gr.Count()
})
.OrderByDescending(t => t.Count); |
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Dim properties = From meta In container.PersistentTypes , p In meta.Members
Select New With {Key .EntityName = meta.Name, Key .MembersCount = meta.Members.Count, Key .FieldName = p.Name, Key .IsArtificial = p.IsArtificial, Key .Description = p.Description, Key .DataAccessKind = p.DataAccessKind, Key .MemberType = If(p.MemberType IsNot Nothing, p.MemberType.Name, Nothing)}
Dim query = (
From p In properties
Group p By p.MemberType Into gr = Group
Select New With {Key .Type = MemberType, Key .Count = gr.Count()}).OrderByDescending(Function(t) t.Count) |
Example 8: Relations
The metadata container also contains info about its relations.The following example shows you how to get all the metadata constraints.
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var query = from meta in container.Constraints
from columns in meta.SourceColumns
select new
{
DestinationTable = meta.DestinationTable.Name,
SourceTable = meta.SourceTable.Name,
Name = meta.Name,
SourceColumn = columns.Name
}; |
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Dim query = From meta In container.Constraints , columns In meta.SourceColumns
Select New With {Key .DestinationTable = meta.DestinationTable.Name, Key .SourceTable = meta.SourceTable.Name, Key .Name = meta.Name, Key .SourceColumn = columns.Name} |
Example 9: Self-Referencing Relations
Maybe you are interested in all types which have self-referencing relations.
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var query = from meta in container.Constraints
where meta.SourceTable.Name == meta.DestinationTable.Name
select new
{
meta.Name
}; |
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Dim query = From meta In container.Constraints
Where meta.SourceTable.Name = meta.DestinationTable.Name
Select New With {Key meta.Name} |
See Also
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