DOC-4510 added add_field example

Author: andy-stark-redis

content/integrate/redis-data-integration/data-pipelines/transform-examples/redis-add-field-example.md

@@ -0,0 +1,160 @@
+---
+Title: Add a new field to a hash/JSON key
+alwaysopen: false
+categories:
+- docs
+- integrate
+- rs
+- rdi
+description: null
+group: di
+linkTitle: Add a new hash/JSON field
+summary: Redis Data Integration keeps Redis in sync with the primary database in near
+  real time.
+type: integration
+weight: 30
+---
+
+By default, RDI adds fields to
+[hash]({{< relref "/develop/data-types/hashes" >}}) or
+[JSON]({{< relref "/develop/data-types/json" >}}) objects in the target
+database that closely correspond to the columns of the source table.
+This example shows how to add extra fields to the target data with the
+[`add_field`]({{< relref "/integrate/redis-data-integration/reference/data-transformation/add_field" >}}) transformation.
+
+The `source` section selects the `customer` table of the
+[`chinook`](https://github.com/Redislabs-Solution-Architects/rdi-quickstart-postgres)
+database (the optional `db` field here corresponds to the
+`sources.<source-name>.connection.database` field defined in
+[`config.yaml`]({{< relref "/integrate/redis-data-integration/data-pipelines/data-pipelines#the-configyaml-file" >}})).
+
+In the `transform` section, the `add_field` transformation adds an extra field called `fullname`,
+which is created by concatenating the existing `firstname` and `lastname` fields using
+an [SQL expression](https://www.simplilearn.com/tutorials/sql-tutorial/concat-function-in-sql).
+
+The `output` section specifies `hash` as the `data_type` to write to the target, which
+overrides the default setting of `target_data_type` defined in `config.yaml`. Also, the
+`output.key` section specifies a custom key format of the form `cust:<customerid>`.
+
+The full example is shown below:
+
+```yaml
+source:
+  db: chinook
+  table: customer
+transform:
+  - uses: add_field
+    with:
+      expression: concat(firstname, ' ', lastname)
+      field: fullname
+      language: sql
+output:
+  - uses: redis.write
+    with:
+      connection: target
+      data_type: hash
+      key:
+        expression: concat(['cust:', customerid])
+        language: jmespath
+```
+
+If you queried the generated target data from the default transformation, you would
+see something like the following:
+
+```bash
+> hgetall cust:14
+ 1) "customerid"
+ 2) "14"
+ 3) "firstname"
+ 4) "Mark"
+ 5) "lastname"
+ 6) "Philips"
+ 7) "company"
+ 8) "Telus"
+ 9) "address"
+10) "8210 111 ST NW"
+.
+.
+```
+
+Using the job file above, the data also includes the new `fullname` field:
+
+```bash
+ 1) "customerid"
+ 2) "14"
+ 3) "firstname"
+ 4) "Mark"
+ 5) "lastname"
+ 6) "Philips"
+ .
+ .
+27) "fullname"
+28) "Mark Philips"
+```
+
+The `add_field` transformation can also add multiple fields at the same time
+if you specify them under a `fields` subsection. The example below is similar
+to the previous one but also adds a `fulladdress` field and uses JSON as the
+target datatype, rather than hash: 
+
+```yaml
+source:
+  db: chinook
+  table: customer
+transform:
+  - uses: add_field
+    with:
+      fields:
+        - expression: concat(firstname, ' ', lastname)
+          field: fullname
+          language: sql
+        - expression: concat(address, ', ', city, ', ', country, ', ', postalcode)
+          field: fulladdress
+          language: sql
+output:
+  - uses: redis.write
+    with:
+      connection: target
+      data_type: json
+      key:
+        expression: concat(['cust:', customerid])
+        language: jmespath
+```
+
+You can query the target database to see the new `fullname` field in
+the JSON object:
+
+```bash
+> JSON.GET cust:14 $.fulladdress
+"[\"8210 111 ST NW, Edmonton, Canada, T6G 2C7\"]"
+```
+
+You can use the `add_field` and `remove_field` transformations together
+to completely replace fields from the source. For example, if you add
+a new `fullname` field, you might not need the separate `firstname` and `lastname`
+fields. You can remove them with a job file like the following:
+
+```yaml
+source:
+  db: chinook
+  table: customer
+transform:
+  - uses: add_field
+    with:
+      expression: concat(firstname, ' ', lastname)
+      field: fullname
+      language: sql
+  - uses: remove_field
+    with:
+      fields:
+        - field: firstname
+        - field: lastname
+output:
+  - uses: redis.write
+    with:
+      connection: target
+      data_type: hash
+      key:
+        expression: concat(['cust:', customerid])
+        language: jmespath
+```