Executing cascading triggers returns error "Subquery returned more than 1 value. This is not permitted"

Question

I cannot seem to get my triggers to work as I expect, with me getting the error "Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <=, >, >= or when the subquery is used as an expression"

I have created several triggers that I use to achieve a cascading delete effect. I am using EF although I can't use it's Cascading Delete fuctionality as there are multiple delete paths in my database.

Anyway every time I delete a company and thus execute the DeleteCompany trigger, I get the above error. I have tried taking out some trigger which I believed to be the cause of the error but I get it every time.

Here are my triggers:

CREATE TRIGGER DeleteCompany 
    ON [dbo].[CompanySet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[EmployeeSet]
    WHERE CompanyId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[TemplateSet]
    WHERE CompanyId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[SettingSet]
    WHERE CompanyId = (SELECT Id FROM deleted) AND EmployeeId = NULL

    DELETE FROM [dbo].[CustomerSet]
    WHERE CompanyId = (SELECT Id FROM deleted)
GO

CREATE TRIGGER DeleteEmployee 
    ON [dbo].[EmployeeSet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[SettingSet]
    WHERE EmployeeId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[FavoriteSet]
    WHERE EmployeeId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[ProjectEmployeeSet]
    WHERE EmployeeId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[ActivityBaseSet]
    WHERE EmployeeId = (SELECT Id FROM deleted)

    DELETE FROM [dbo].[ActivityReportSet]
    WHERE EmployeeId = (SELECT Id FROM deleted)
GO

CREATE TRIGGER DeleteRole
    ON [dbo].[RoleSet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[AccountRoleSet]
    WHERE RolesId = (SELECT Id FROM deleted)    
GO

CREATE TRIGGER DeleteCustomer
    ON [dbo].[CustomerSet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[ProjectSet]
    WHERE CustomerId = (SELECT Id FROM deleted) 
GO

CREATE TRIGGER DeleteProject
    ON [dbo].[ProjectSet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[TemplateSet]
    WHERE ProjectId = (SELECT Id FROM deleted)  

    DELETE FROM [dbo].[ActivityBaseSet_Activity]
    WHERE ProjectId = (SELECT Id FROM deleted)  

    DELETE FROM [dbo].[ActivityReportSet]
    WHERE ProjectId = (SELECT Id FROM deleted)  

    DELETE FROM [dbo].[FavoriteSet]
    WHERE ProjectId = (SELECT Id FROM deleted)  

    DELETE FROM [dbo].[ProjectEmployeeSet]
    WHERE ProjectId = (SELECT Id FROM deleted)  
GO

CREATE TRIGGER DeleteSettingDefinition
    ON [dbo].[SettingDefinitionSet]
    INSTEAD OF DELETE
AS
    DELETE FROM [dbo].[SettingSet]
    WHERE SettingDefinitionId = (SELECT Id FROM deleted)    
GO

CREATE TRIGGER DeleteTemplate
    ON [dbo].[TemplateSet]
    INSTEAD OF DELETE
AS
    UPDATE [dbo].[ActivityReportSet] SET [dbo].[ActivityReportSet].TemplateId = NULL
    FROM deleted
    WHERE [dbo].[ActivityReportSet].TemplateId = deleted.Id
GO

Am I missing something here?

Answer 1

Can you replace all your "=" with "IN" operator for your sub queries like:

DELETE FROM [dbo].[EmployeeSet]
    WHERE CompanyId IN (SELECT Id FROM deleted)