From 1e53b3895cf57e9e1237c9c9ee3b20ec3ca9e48a Mon Sep 17 00:00:00 2001
From: Pablo Martin <pablo.martin@lolamarket.com>
Date: Thu, 2 Nov 2023 17:05:44 +0100
Subject: [PATCH] Thingies

---
 .../dbtlearn/snapshots/scd_raw_listings.sql   | 17 +++++++++++
 notes/8.md                                    | 28 ++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 code_thingies/dbtlearn/snapshots/scd_raw_listings.sql

diff --git a/code_thingies/dbtlearn/snapshots/scd_raw_listings.sql b/code_thingies/dbtlearn/snapshots/scd_raw_listings.sql
new file mode 100644
index 0000000..4108a21
--- /dev/null
+++ b/code_thingies/dbtlearn/snapshots/scd_raw_listings.sql
@@ -0,0 +1,17 @@
+{% snapshot scd_raw_listings %}
+
+{{
+    config(
+        target_schema = 'dev',
+        unique_key = 'id',
+        strategy = 'timestamp',
+        updated_at = 'updated_at',
+        invalidate_hard_deletes = True
+    )
+}}
+
+SELECT *
+FROM
+    {{ source('airbnb', 'listings')}}
+
+{% endsnapshot %}
diff --git a/notes/8.md b/notes/8.md
index 22ed54d..f96b728 100644
--- a/notes/8.md
+++ b/notes/8.md
@@ -47,4 +47,30 @@ Bear in mind that how to define the strategy to determine what should be loaded
 Seeds are local files that you upload to a DWH from dbt. You place them as CSVs in the `seeds` folder.
 
 
-Sources are an abstraction layer on top of the input tables. They are not strictly necessary, but can help make the project more structured. To create sources, you create a `sources.yml` file and place it in the `models` dir.
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+Sources are an abstraction layer on top of the input tables. They are not strictly necessary, but can help make the project more structured. To create sources, you create a `sources.yml` file and place it in the `models` dir. Here, you can reference models created in the `models` dir to mark them as sources. You can reference sources in other models like this:
+
+```python
+{{ source('domain_name', 'source_name')}}
+```
+
+Sources can define _freshness_ constraints that will provide warnings or errors when there is a significant delay.
+
+ 
+## Snapshots
+
+Snapshots are a way to build SCD2s. There are two strategies to get this done:
+  - Timestamp: all records have a unique key and an `update_at` field. dbt will consider a new record is necessary in the SCD2 whenever the `updated_at` field increases.
+  - Check: dbt will monitor a set of columns and consider any changes in any of the columns as a new version of the record.
+
+Snapshots get defined with a sql file in the `snapshots` folder using the `snapshot` macro block.
+
+Once snapshots are defined, "snapshooting" can be triggered at any time by running `dbt snapshot`. dbt will create the SCD tables in the defined schema and play the `valid_from`, `valid_to` game whenever changes are detected.
+
+## Tests
+
+There are two kinds of tests:
+
+- Singular tests: you make any `SELECT` statement you want. If the `SELECT` statement is run and any data is found, the test is considered failed. If the statement is run and no rows are returned, the test is considered passed.
+- Built-in test: just a bunch of typical stuff: uniqueness, nullability, enum validations and relationship (referential integrity)
+
+You can also define your own custom generic tests.
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