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Entity Framework Extensions ToSelfHierarchyList

Description

The ToSelfHierarchyList method extend your Entity Framework DbContext to let you easily include a self hierarchy relationship.

var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(x => x.Boss);

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Real Life Scenarios

Include boss, and add them in the returned list

Like the Include method, by default, the entity from the hierarchy is materialized but not part of the returned list.

The option FlatListRecursionLevel let you include boss in returned list. Use Int.MaxValue to return all levels.

  • FlatListRecursionLevel = 0: will return employee only.
  • FlatListRecursionLevel = 1: will return employee with direct boss.
  • FlatListRecursionLevel = 2: will return employee with direct boss and their boss.
var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(x => x.Boss, 
		options => options.FlatListRecursionLevel = 1);

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Include boss, and filter them

The employee can be filtered as you normally do within Entity Framework.

The SelfHierarchyQuery option let you filter the query that retrieve boss.

// The "Boss_2" will not be retrieved
var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(x => x.Boss, options => 
		options.SelfHierarchyQuery = q => q.Where(x => !x.Name.Contains("2")));

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Include boss, but only direct one

By default, the library make 10 recursions when retriving the boss hierarchy.

The MaxRecursion option let you limit the number of recursion. By specifying a MaxRecursion = 1, you only retrieve direct boss of your employee.

// The CEO will not be retrieved
var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(x => x.Boss, options => 
		options.MaxRecursion = 1);

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Include boss, but with custom mapping

If your entity doesn't have navigation property toward boss or employee, it's impossible to use the join expression.

The ColumnMappings option let you specify yourself the mapping. Careful, the column name and not the property name must be used.

var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(null, options => {
		options.ColumnMappings.Add("BossID", "EmployeeID");
		options.FlatListRecursionLevel = int.MaxValue;
	});

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Include boss, but with an inverse navigation

If your entity has only a reference to a list of employees and no navigation property toward the boss, it's impossible to use the JoinExpression to include the boss.

The InverseMapping option let you specify a join expression toward employee but to inverse it. So, instead of retrieving their employees, you will retrieve the boss.

var employees = context.Employees.Where(x => x.Name.StartsWith("Employee_"))
	.ToSelfHierarchyList(x => x.Employees, options => {
		options.InverseMapping = true;
		options.FlatListRecursionLevel = int.MaxValue;
	});

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Documentation

ToSelfHierarchyList

Methods
Name Description Example
ToSelfHierarchyList(Expression<Func<T, object>> joinExpression) Materialize a list of entity and include the self hierarchy. Try it
ToSelfHierarchyList(Expression<Func<T, object>> joinExpression, Action<SelfHierarchyListOptions<T>> options) Materialize a list of entity and include the self hierarchy. Try it
Options
Name Description Example
ColumnMappings Gets or sets the column mappings. Try it
FlatListRecursionLevel Gets or sets the flat list recursion level. Default = 0 which return only item from the query. Try it
InverseMapping Gets or sets a value indicating whether the mapping is inversed. Try it
JoinExpression Gets or sets the join expression. Try it
MaxRecursion Gets or sets the maximum recursion to perform. Default = 10. Try it
SelfHierarchyQuery Gets or sets the filtered self hierarchy query to use. Try it

Limitations

  • Support EF6 only
  • Support SQL Server only

EF Core support is under development.


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