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Title
# ask-ai
s

Sean Pool

03/13/2024, 9:59 PM
@Scout I am configuring a dagster job that is comprised of the following steps… Ideally I want it to run sequentially but I don’t know how to configure the job without it concurrently beginning each query as soon as the job is started due to the lack of dependencies between the two. How can I implement this into a sequential job? Example query generate1 write1 query2 generate2 write2 query3 generae3 write3 query4 generate4 write4 query uploadtos3
s

Scout

03/13/2024, 9:59 PM
To configure a Dagster job to run steps sequentially, you can define dependencies between the steps to ensure that each step waits for the previous step to complete before starting. In Dagster, you can define these dependencies within a job by specifying the inputs and outputs of each step, which are known as assets when using the asset-based APIs. Here's a high-level example of how you might define a job with sequential steps using assets:
Copy code
python from dagster import asset  @asset def query1():     # Your query logic here     return query1_result  @asset def generate1(query1_result):     # Your generate logic here, using query1_result     return generate1_result  @asset def write1(generate1_result):     # Your write logic here, using generate1_result     pass  # Assuming this step doesn't produce an output  # Repeat the pattern for query2/generate2/write2, etc.  @asset def upload_to_s3(write1_result, write2_result, write3_result, write4_result):     # Your upload logic here, using the results from all write steps     pass
In this example, each
generate
asset depends on the result of the corresponding
query
asset, and each
write
asset depends on the result of the corresponding
generate
asset. Finally, the
upload_to_s3
asset depends on the results of all
write
assets. By defining these dependencies, Dagster ensures that the assets are executed in the correct order, with each step waiting for the necessary inputs to be available. This is a simplified example, and in a real-world scenario, you would include the actual logic for querying, generating, writing, and uploading within the functions. Additionally, you might need to pass configuration or resources to your assets, which you can do using the
@asset
decorator's parameters. Remember that the actual implementation details will depend on your specific use case, including how you handle inputs, outputs, and any external systems you interact with. The documentation provides more detailed guidance on defining assets and dependencies, which you can refer to for more in-depth examples and best practices.
s

Sean Pool

03/13/2024, 10:05 PM
@Scout These are jobs, and each step does not depend on the data from the prior steps, it simply requires that it be executed sequentially. How can I handle these dependencies if the functions dont take the result of the prior step as input
s

Scout

03/13/2024, 10:05 PM
If the steps in your job do not depend on the data from the prior steps but still need to be executed sequentially, you can use "Nothing" dependencies to enforce execution order without passing data between the steps. The "Nothing" type in Dagster is a special type that indicates an op (or asset) has a dependency on another op (or asset) without needing its output. Here's an example of how you might define a job with sequential steps using "Nothing" dependencies:
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python from dagster import job, op, In, Nothing  @op def step1():     # Your logic for step1  @op def step2(start: Nothing):     # Your logic for step2  @op def step3(start: Nothing):     # Your logic for step3  @op def step4(start: Nothing):     # Your logic for step4  @job def sequential_job():     step1_result = step1()     step2(start=step1_result)     step3(start=step2())     step4(start=step3())
In this example,
step2
,
step3
, and
step4
each have an input parameter
start
of type
Nothing
. This parameter is used to establish a dependency on the previous step. When defining the job, you pass the output of each step (even though it's not used) to the next step to enforce the execution order. The
Nothing
type tells Dagster that an op should wait for the specified dependency to complete before it begins execution, even though it does not consume any actual output from that dependency. This way, you can ensure that your steps are executed in the desired sequence without needing to pass data between them.