Initial version of query generation for Postgres and MS SQL

[JelteF]

This is an initial version of the query generation approach proposed in this RFC: https://github.com/Azure/project-hawaii/pull/18

It allows for JOINs to happen automatically.

There's quite some features this does not implement yet, some of
which would have been possible with the previous approach of
hardcoded queries:

1. Parameters
2. Selecting a single top row (this pretty much requires parameters)
3. Putting a LIMIT on rows
4. ORDER BY primary key
5. One-To-One relationships
6. Many-To-Many relationships

All these features are postponed for follow up PRs, so they can easily be worked on
concurrently by different people. The code in this PR provides a good base.

The database schema I've been using to test this can be found in the books.sql file.

A basic GrahpQL query like this works with the code:

query {
    getBooks {
        id
        title
        publisher_id
        publisher {
            id
            name
        }
        reviews {
            id
            content
        }
    }
}

But a crazy query like this also works (but it is pretty slow):

query {
  getBooks {
    id
    title
    publisher_id
    publisher {
      id
      name
      books {
        title
        publisher {
          books {
            publisher {
              books {
                publisher {
                  books {
                    publisher {
                      books {
                        publisher {
                          books {
                            publisher {
                              books {
                                publisher {
                                  books {
                                    publisher {
                                      books {
                                        publisher { 
                                          books {
                                            publisher {
                                              name
                                            }
                                          }
                                        }
                                      }
                                    }
                                  }
                                }
                              }
                            }
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
        
      }
    }
    reviews {
        id
        content
    }
  }
}

[jarupatj]

what the query generated for the crazy example that you gave? Can you add tests?

[jarupatj]

How many queries will be generated and executed? How do we handle N+1 problem in GraphQL? #Resolved

[Aniruddh25]

Did an initial review, need to still look deeper in the SqlQueryStructure and builders.
Have some changes requested till then.

[jarupatj]

Nvm. RFC answered this question.

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In reply to: 940620331

[Aniruddh25]

Perhaps, we need to identify the Many:Many relationship, get that from metadata and based on the query fieldName do an INNER JOIN if needed, check the suggestion on the RFC...

[JelteF]

I think this PR is already much bigger than I would like it to be. I'd like to punt on the Many-To-Many code for the next iteration.

[jarupatj]

//TODO: Try to avoid additional deserialization/serialization here.

Can we create a work time to track this work?

[Aniruddh25]

Please merge with the FindQueryStructure class I added in the PR #98

[seantleonard]

nit: in the PR description, the sample GraphQL queries have (first:3) . May want to remove for now, so sample queries can be directly tested. Currently, as your PR notes, Putting Limit on rows is not supported yet.

[seantleonard]

Thanks for adding additional tests and addressing comments. Just a few more questions added from me and Jarupat, but functionality wise, is working in my few queries used against your provided GQL and SQL schemas and got all the integration tests passing locally.

[jarupatj]

        Utf8JsonWriter writer = new(stream, new JsonWriterOptions { Indented = false });

Can you add "using" for both MemoryStream and Utf8JsonWriter. Both of them implements IDisposable

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Refers to: DataGateway.Service.Tests/MsSqlTests/MsSqlRestApiTests.cs:153 in 0eae5f1. [](commit_id = 0eae5f1, deletion_comment = False)

[jarupatj]

I signed off with some additional comments. I enjoyed reading this code. Thanks!

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In reply to: 985188021

[jarupatj]

[seantleonard]

Note for others: Since Parameters are not currently supported in this PR and will be introduced in a later PR, REST functionality will temporarily be non-functional. REST requests, currently, FindById, depend on parameters, which is not populated during MsSqlQueryBuilder.Build(SqlQueryStructure structure) method.

The query generated from the request:
https://localhost:5001/books/id/2
will look something like:
"SELECT TOP 1 * FROM [books] AS [books] WHERE [books].[id] = @param1"

[JelteF]

Note for others: Since Parameters are not currently supported in this PR and will be introduced in a later PR, REST functionality will temporarily be non-functional. REST requests, currently, FindById, depend on parameters, which is not populated during MsSqlQueryBuilder.Build(SqlQueryStructure structure) method.

@seantleonard Actually REST functionality still works. Parameters are not used during query building but during query execution.

[seantleonard]

Note for others: Since Parameters are not currently supported in this PR and will be introduced in a later PR, REST functionality will temporarily be non-functional. REST requests, currently, FindById, depend on parameters, which is not populated during MsSqlQueryBuilder.Build(SqlQueryStructure structure) method.

@seantleonard Actually REST functionality still works. Parameters are not used during query building but during query execution.

My bad. Yes I got REST working. For some reason, though the errors were because of non filled in parameters, and only saw the true error (SQL login issue in connection string) from BananaCakePop interface. I can look into better logging errors like login issues into the console for REST side of code.

[seantleonard]

This piece makes sense now. This is to accommodate dynamically building query and all conditions can be added like and X ?

https://stackoverflow.com/questions/242822/why-would-someone-use-where-1-1-and-conditions-in-a-sql-clause