Allow creation of a DbCommand from an EF IQueryable

[ajcvickers]

See #19335

For example:

var query = context.Blogs.Where(b => b.Published);
var command = query.CreateDbCommand();

Things to note:

• The command providers access to the SQL query string and parameters.
• The created command is not the actual command that EF will use if the query is then executed. A new command will be created for this, but using the same mechanism.
• The created command can likely be executed, but will be doing so outside of the normal EF environment and so may not have exactly the same behavior.

[Giorgi]

Looking at the Source of CreateDbCommand it looks like that the command must be executed before the cache is populated. Is there a way to get the command without actually executing the IQueryable ?

[ajcvickers]

@Giorgi What "cache" are you referring to?

[Giorgi]

I mean this code:

efcore/src/EFCore.Relational/Query/Internal/QueryingEnumerable.cs

Line 88 in b3a89d0

public virtual DbCommand CreateDbCommand()

[Giorgi]

The code that I linked to in my first comment calls source.Provider.Execute so I guess that is needed to populate the _relationalCommandCache

[ajcvickers]

@Giorgi The code for CreateDbCommand does not execute the command. Also, as far as I can tell, it will populate/use the command cache.