Can I join work without foreign key?

Can I join work without foreign key?

Without the foreign key you could have “orphaned” children that point at a parent that doesn’t exist. You need two columns of the same type, one on each table, to JOIN on. Whether they’re primary and foreign keys or not doesn’t matter. You don’t need a FK, you can join arbitrary columns.

How do I join two tables without foreign key?

JOIN Tables Without Foreign Key In SQL Server

  1. Create three SQL tables in SQL Server 2014 or higher. I have created 3 tables as mentioned below with their respective code.
  2. Step 2 – Insert some demo data to all three tables. Insert records into the employee table. /*INESRT VALUES IN EMPLOYEE TABLE*/

Do we need foreign key for join?

While foreign keys and primary keys are not strictly necessary for join queries, they greatly help by telling you what to expect. For instance, you can be sure that records referenced from table A will always be present in table B – so a join from table A will always find something in table B.

Does Entity Framework support foreign keys?

Relationships in EF. In relational databases, relationships (also called associations) between tables are defined through foreign keys. In Entity Framework, an entity can be related to other entities through an association or relationship.

Can foreign key be repeated?

By default there are no constraints on the foreign key, foreign key can be null and duplicate. while creating a table / altering the table, if you add any constrain of uniqueness or not null then only it will not allow the null/ duplicate values.

Can a table be without foreign keys?

Foreign Keys without the constraints You could instead configure two tables such that one refers to the other, but without any defined foreign key. You could even make it another data type entirely, such as a varchar, while the User table’s ID column might be an int or Guid/uniqueidentifier.

Can a table have foreign key without primary key?

A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table. So in your case if you make AnotherID unique, it will be allowed.

Can we create foreign key without primary key?

If you really want to create a foreign key to a non-primary key, it MUST be a column that has a unique constraint on it.

How do I set foreign key in Entity Framework?

Left as it is, Entity Framework Core will create an AuthorFK field and an AuthorId field which it will configure as a foreign key:

  1. public class Author.
  2. {
  3. public int AuthorId { get; set; }
  4. public string FirstName { get; set; }
  5. public string LastName { get; set; }
  6. public ICollection Books { get; set; }
  7. }

How does Entity Framework handle foreign key?

The ForeignKey attribute is used to configure a foreign key in the relationship between two entities in EF 6 and EF Core. It overrides the default conventions. As per the default convention, EF makes a property as foreign key property when its name matches with the primary key property of a related entity.

Can foreign key null?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table).

When to use join clause in Entity Framework?

Entity Framework Joining. Joining. In SQL, a JOIN clause is used to combine data from two or more tables, based on a related column between them. Similarly, in Entity Framework, the LINQ Join is used to load data from two or more tables.

How are foreign keys defined in one to many relationships?

In a one-to-many relationship, the foreign key is defined on the table that represents the many end of the relationship. The many-to-many relationship involves defining a third table (called a junction or join table), whose primary key is composed of the foreign keys from both related tables.

How are foreign keys used in independent associations?

In both foreign key and independent associations, concurrency checks are based on the entity keys and other entity properties that are defined in the model. When using the EF Designer to create a model, set the ConcurrencyMode attribute to fixed to specify that the property should be checked for concurrency.

How does relationship fix up work in Entity Framework?

When you change the relationship of the objects attached to the context by using one of the methods described above, Entity Framework needs to keep foreign keys, references, and collections in sync. Entity Framework automatically manages this synchronization (also known as relationship fix-up) for the POCO entities with proxies.