Styjun

I have to design a multi-tenant application, I need to have custom fields for each tenant in the same model.

Customer 1 need to use some custom field, Customer 2 need to manage other fields in the same table and so on..

This is an example:
the same table (ticket) has a common (base) field list, then each tenant should be have his additional columns in the model:

I would like to implement a EF Code first .Net Core web application.

namespace Models.Base

 public class TicketBase
 
 public int Id get; set; 
 public string Description get; set; 
 public Datetime CreationDate get; set; 
 

Tenant 1

namespace Models.Tenant1

 public class Ticket : TicketBase
 

 public string CustomerName get; set; 
 public Datetime DateCustomerCall get; set; 
 

Tenant 2

namespace Models.Tenant2

 public class Ticket : TicketBase
 

 public string AnotherDescription get; set; 
 public Datetime AnotherDate get; set; 
 

Is it correct to design the model this way or there are different approaches to this very common problem?

IMHO, In SaaS, having a single code base and flexible configuration / extension for mutli-tenancy is the key to success.

To enable custom fields per tenant, the business model will have to have a fixed set base fields. The custom fields will have to be stored by entityid and tenantid in a separate table.

Your tables could look like the ones given below. This model is preferred so that having a generic extension table will result in less scalability and could soon be filled with the data volume as usage goes up.

Ticket

TicketExtn (extension table containing custom fields by tenant and entity)

The TicketExtn table will contain fields like

TicketId
TenantId
FieldId
FieldValue
FieldDataType

etc
When we try to get the data for the Ticket entity, we will also be getting the data from the TicketExtn table and be setting the fields in the model.

The BaseModel will look like the one given below

public class ExtendedField

 public Guid Id get; set; 
 public string FieldName get; set; 
 public Guid DataTypeId get; set; 
 /// <summary>
 /// Can also be a typed class, this is just for reference
 /// </summary>
 /// <value>The field value.</value>
 public string FieldValue get; set; 
 /// <summary>
 /// Incase of using string for fieldvalue, the string to format the value as per the required datatype 
 /// will be provided here.
 /// </summary>
 /// <value>The field value format string.</value>
 public string FieldValueFormatString get; set; 


public class BaseModel

 Dictionary<string, ExtendedField> ExtendedRows get; set; 


public class Ticket : BaseModel

 public int Id get; set; 
 public string Description get; set; 
 public DateTime CreationDate get; set; 

In your services layer, there will be logic to fill these extended rows. Its better to have the logic for the filling up of the extended rows generic so that for any number of entities, this logic can be re-used.

HTH