Relationships

* To avoid redundancy and inconsistency we have to use relationships in sfdc. 
* Redundancy: Repeating records/data in multiple locations is called redundancy.
* Inconsistency: Due to the repetition of the data, if we delete data at one location in other  location the data exists due to that inconsistency will arise.

 In SFDC, we have 5 types of relationships:

1. Self Relationship

2. Look-up Relationship

3. Master Detail Relationship

4. Many to Many Relationship

5. Hierarchical Relationship

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1. Self Relationship:

*It is the relationship between two fields of the same sObject.

* From one field value of the sObject we will derive another field value of the sObject.

* Using Formula data-type we can achieve self relationship. 

2. Look-up Relationship:

* It is the relationship between two sObjects provided one is child which contains link to the parent and another one is parent which contains physical record.

 *If we delete physical record in parent object all the referencing child fields(not entire record) get deleted.

*If the relationship is not mandatory in that case we have to use look-up relationship.
* Up to 25 look-up relationships we can create for single sObject. 

3. Master Detail Relationship:

* It is the relationship between two sObjects provided one is child which contains link to the parent and another one is parent which contains physical record.
*If we delete physical record in parent object all the referencing child records(entire records) also get deleted.

*If the relationship is mandatory in that case we have to use master-detail relationship.

* In master-detail parent object we can create roll-up summary field.

*It is not possible to create master detail relationship if the child object has records in it, if it is empty then only we can create master-detail relationship.

* We can convert master-detail to look-up easily without any restrictions.
* up to 2 master-detail relationships we can create for single sObject.
* a detail record automatically inherits the sharing setting of its parent.

4. Many to Many Relationship:

*If one sObject having two master-detail relationships is called Junction Object.

*For a junction object no need to create tab.

* Junction object can't be on the master side of another master-detail relationship.
*The relationship between two master objects having a common child object i.e. junction object is called many to many relationship.

*many to many relationship form indirectly. 
*We can't create a many to many relationship, If two master-detail relationships on the junction object can't have the same master object.

*To exchange data between two master objects using many to many relationship we have to use related list.

5. Hierarchical Relationship:

* It is the relationship between the users of the organization.

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Important points to consider:

* We can convert look-up to master-detail only when all the fields in the look-up relationship populate (fill) with the values.

*If we delete a child sObject and undelete it again then all the master-detail relationships will be converted to look-up relationships.

*It is not possible to delete child sObject if the parent has Roll-up summary field, because parent is using child object information.

*It is not possible to delete parent objects because child sObject using parent sObject information (master-detail parent object).
* If the custom object is on the detail(child) side of the master-detail relationship, it can't be the master side of a different master-detail relationship.
* Standard objects can't be on the detail side of a custom mater-detail relationship.

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Interview Questions:

Q. When to use Look-up and Master-detail relationships?

A.  * If we need to create roll-up summary field and if we need many to many relationship in that case we have to use master-detail relationship.

*For master-detail, relationship is mandatory.

*For look-up, relationship is not mandatory.

*First we have to create look-up then if the master-detail relationship is necessary for that sObject then we have to convert it to master-detail relationship.