Add crossJoin, innerJoin, leftJoin, rightJoin and fullJoin.

[mahdiaslami]

• Cross Join
• Inner Join: Add join().
• Add innerJoin() helper.
• Left Outer Join: Add leftJoin().
• Right Outer Join: Add rightJoin().
• Full Join: Add fullJoin().
• Resolve all todos.

[mahdiaslami]

Cross join added before.

[mahdiaslami]

Problem

• What should we do to prevent overwriting properties?
• How should we compare two columns with the same name?

1. Force using an alias in join.

query(childs)
    .join(parents, 'p')
        .on('parent_id').col.equal('p.id')
    .get()

And result is like:

const r = {
    id: 1,
    name: 'foo',
    /* [[OTHER CHILD PROPS]] */

    p: {
        id: 2,
        name: 'bar',
        /* [[OTHER PARENT PROPS]] */
    }
}

2. Force using an alias for join and query when using join.

query(childs, 'c')
    .join(parents, 'p')
        .on('c.parent_id').col.equal('p.id')
    .get()

And result is like:

const r = {
    c: {
        id: 1,
        name: 'foo',
        /* [[OTHER CHILD PROPS]] */
    },
    
    p: {
        id: 2,
        name: 'bar',
        /* [[OTHER PARENT PROPS]] */
    }
}

3. Implement both ways 1 and 2, And make them optional.

• If a developer does not provide both aliases, overwrite columns with the same name.
• When the column name in the on() method is the same as the column name in the on().col.<condition>() method then the first column always belongs to the main array. and the second column always belongs to the joined array.

[mahdiaslami]

I think this issue is too big and I must separate it into smaller issues that will handle in one sprint.

• Add Full Outer Join. #42
• Add alias for Join and Query main array. #43
• Find TODOs and resolve them. #44