Controversial: Allow parameter values to be obtained along with query string

[ajcvickers]

Issue #6482

var parameters = new Dictionary<string, object>();
var queryString = queryable.ToQueryString(parameters);

Not 100% convinced we should do this. Here's my thinking:

• This can be useful for diagnostics/testing by providing the parameter values in a machine-readable, non string converted form. For example, imagine a profiling tool that can read the dictionary and make the parameter values available to run perf testing, get query plan, etc.
• On the other hand, this could be used by people who want to use EF only to generate queries which are then executing somewhere else. This is not a goal of EF and the queries may not run in some other context, so it could give a false impression of what EF is designed to do.
• But if we don't do this publicly, then I think the discussion on Provide a simple way to get SQL statements generated from EF queries #6482 indicates that people are going to continue to hack EF into doing it. This could end up being more painful than just supporting the feature.

[roji]

I don't think this adds anything more controversial beyond basic ToQueryString - if we allow getting SQL out. why not also parameters... So seems OK to me.

A thought... If we do this, should we stop adding parameters into the returned SQL as comments? I'm assuming that if people simply want to log SQL (and parameters), that's what we have logging for (including the new simple logging). So this would be more for programmatic access (profilers etc.), in which case the extra comments don't necessarily make sense?

[ajcvickers]

@roji It's more controversial because it makes it even easier for people to abuse the API and use it for SQL execution in an application.

[ajcvickers]

Notes from design meeting:

• We will keep this API public and call it ToQueryString
  • We also discussed calling it ToDebugString, but that's less specific and discoverable. Also, other ToDebugString methods are internal.
• We will not make this relational-specific
  • Non-relational providers may also have reasonable strings for their queries
• We will remove the parameters--i.e. this PR
  • Instead Even more controversial: Allow creation of a DbCommand from an EF IQueryable #19335 can be used to get the parameters for relational providers
  • This also allows all parameter facets to be obtained
• We will change the format of comments based on the suggestion here: DebugView for query and simple way to get SQL from an EF LINQ query #19324 (comment)
  • However, this is SQL Server specific, so the format only changes for SQL Server
  • We will still use comments since this isn't actually SQL that EF would normally generate. Changed my mind on this part.

[ajcvickers]

Superseded by #19368