Learning Neo4j Graphs and Cypher : Update/Delete | packtpub.com

PROFESSOR: In this
section, we're

going to be talking about
updating data, deleting data,

and we're going to
learn a few new commands

and functions within Neo4j.

In this first section,
we'll be talking

about updating existing
nodes and relationships,

using new keywords to find
data, deleting nodes, detaching

relationships, and detaching
and deleting nodes.

In this first
video, we'll go over

some of the capabilities of the
MERGE statement in preparation

of the rest of the video.

And then we'll look at
the commands of MERGE,

the conditions that happen
when you create a new node,

as well as the conditions
that happen when

you match an existing node.

We'll also use MERGE
where we could use MATCH

and SET to change attributes.

To review, we have
a basic data model

set up with actors and movies.

Our goal was to solve the six
degrees of Kevin Bacon problem.

This first MERGE statement
will find an actor with the ID1

and will show its information.

In the Neo4j web
browser, we can type

merge parentheses lowercase A
as in Alias, actor as the label.

We can specify the ID of 1 to
filter, and we can return a.

When we execute
this statement, we

should receive one node
representing Kevin Bacon.

We can look in the rows, the
texts to show more raw results.

We can show all the attributes
for this Kevin Bacon actor.

We can also use MERGE
to create new nodes.

Here we'll create a new
actor node with the ID of 99

and we'll return it.

Again, we'll type merge, a,
an Alias actor, ID of 99,

and will return a.

We know this data doesn't
exist since we only set up--

we know this data doesn't exist
because we only set up actors 1

through 7 or so.

So when we execute this,
it will create a new node

with no attributes,
oops, because we only

supplied the ID parameter
or the ID attribute

in the MERGE statement.

What we should have done
to create a new actor

node with more attributes
is specify those attributes

within the MERGE statement.

Here we're going to make
an actor with the ID of 99

and the name of George George.

When we execute that
Cipher statement,

we'll see the new actor
created with the ID of 99.

Now the problem is we ran the
merge twice with an ID of 99.

So if we run it again
without the name,

this should match on all
nodes with the ID of 99,

and in this case, we will
get our two actor nodes.

The MERGE statement can also
act like an insert or update

statement or construct within
traditional database systems.

Using the MERGE
statement, you can

create a condition
called ON CREATE

and you can execute or
update specific values.

You can also set the
condition for ON MATCH where

you can do something else.

In this case, we'll create a
new actor with the ID of 98.

When it's created, we'll
set the name to Mark Hamill

and we'll add a counter field.

We haven't done this yet, but
we'll add a counter field of 0.

If we rerun this MERGE statement
and the condition of ID 99

is already met, we'll execute
the statements ON MATCH section

where we'll set the counter
to the counter plus 1,

effectively incrementing
the counter every time

we merge on this node.

Let's try it out.

You'll see here we can
type this MERGE statement,

merge, actor ID 98.

ON CREATE, we'll set the name to
Mark Hamill with a counter of 0.

ON MATCH, we'll set the
counter to counter plus 1

and we'll return the actor node.

Here we'll execute it and
we should see our new node.

If we look at the raw results
we'll see a counter of 0.

So using the browser.

We can click on the
Cipher statement again.

Press it again, our
counter will increment.

And every time we
execute this since we're

matching on the ID of 98,
our counter increments.

So this shows the
two conditions we

have used in the MERGE statement
ON CREATE and ON MATCH.