Mastering Home Assistant Templates: We got Errors

In this segment, the video discusses common errors encountered when working with Home Assistant templates and how to address them. It highlights a recent error introduced in the 2023.5 update, which generates messages indicating that a sensor has a non-numeric value when it should be numeric. The video provides a solution by suggesting the removal of the 'unit of measurement' from non-numeric template sensors. Additionally, it covers the 'unknown error' that occurs when template sensors are based on other sensors' states and how to use a 'has value' function to check for valid states before using them in Jinja templates. The segment also touches on setting up basic if-else statements and creating a Home Assistant sensor with a state that never expires.

This paragraph delves into the issue of sensor state expiry in Home Assistant, which can lead to gaps in sensor data and subsequent errors when performing calculations within templates. The video explains that Home Assistant sensors' states expire after a certain period to avoid displaying stale data. It demonstrates how to use the 'has value' function in conjunction with an if statement to check if a sensor has a valid state before using it in a template. The solution involves adding decision logic to the template to avoid errors when the sensor state is unknown or unavailable. The video also provides a workaround using MQTT to save sensor data and prevent state expiry, by publishing sensor updates to an MQTT topic with a retained flag set to true, ensuring the last value is retained indefinitely.

Building upon the previous discussion, the video script outlines the process of creating an MQTT sensor to retain the state of a sensor indefinitely. It guides the viewer through setting up an automation that triggers whenever a specific sensor updates and publishes its value to an MQTT topic. The script then details how to define an MQTT sensor in the 'mqtt.yaml' file, which subscribes to the topic and retains the last published value. This approach ensures that even if the original sensor's state expires, the MQTT sensor retains the last known value, thereby avoiding errors and gaps in the data.

The final paragraph of the script previews upcoming content in the video series, focusing on mastering Home Assistant templates. It promises to cover more advanced topics such as building state-based template entities with decision logic, creating complete sensors with their own attributes, and working with dates. The video aims to guide viewers in automating more complex and dynamic aspects of their smart homes, making the process of managing home automation tasks more efficient and less tedious.