Add support to use current values in insert Mysql/Postgres

[apellizzn]

In Mysql / Postgres add support to update record during INSERT on conflict / duplicate key using current values, implements, fixes #3047

[jsnick]

I think there is atomic update case like column = column + 1

[apellizzn]

@jsnick I think we can use column = column + 1 when we want to update the value based on the current value in the database.
What i am doing with this PR is to update the value based on the current record that i am trying to insert.
Using counter = counter + 1 will produce

| id | counter |
|----|---------|
| 1  | 5       |

INSERT INTO foo (id, counter) VALUES (1, 10) ON DUPLICATE KEY UPDATE counter = counter + 1 

| id | counter |
|----|---------|
| 1  | 6       |

Using counter = VALUES(counter) will produce

| id | counter |
|----|---------|
| 1  | 5       |

INSERT INTO foo (id, counter) VALUES (1, 10) ON DUPLICATE KEY UPDATE counter = VALUES(counter)

| id | counter |
|----|---------|
| 1  | 10      |

[marshall007]

It would be nice if a high-level conflict: 'ignore' | 'replace' | 'error' option were also exposed on EntityManager's save/update/insert APIs.

[apellizzn]

@marshall007 Sure, to me this sounds like another PR i would like to merge this one first.

[pleerock]

QueryBuilder is a complex task since we replace property names in database names and use property names in queries in most of places. In this case looks like we have to use database names, and its confusing.

Lets merge it for now, but someday we'll need to figure out what to do with this confusion.

Thank you for the contribution!

[pleerock]

ooups looks like a conflict, can you please resolve it?

[apellizzn]

@pleerock Sorry for the delay, resolved :)

[pleerock]

so, why its needed?)

[apellizzn]

Because in some cases when you actually insert multiple rows which cause a conflict entity is not defined, so therefore line 595 will break value = entity[this.propertyName];

Database with columns c1, c2, c3 with a unique index on c1 and the following data

| A (c1) | Foo (c2) | Bar (c3) |

If i try to insert the following

| A | Foo2 | Bar2 |
| A | Foo3 | Bar3 |

I just want the database to be | A | Foo3 | Bar3 | i guess this has something to do with the fact that you are actually trying to insert N rows but returning N-1

[pleerock]

mm not sure I got it, but okay, lets merge it

[pleerock]

Thank you!