Entity Framework Core – Part 5

This will be the fifth post in a series of posts about bringing the features that were present in Entity Framework pre-Core into EF Core. The others are:

Part 1: Introduction, Find, Getting an Entity’s Id Programmatically, Reload, Local, Evict
Part 2: Explicit Loading
Part 3: Validations
Part 4: Conventions

This time I’m going to talk about something that is often requested: how can I get the SQL string for a LINQ query? If you remember, in the pre-Core days you had to do some reflection in order to get the underlying ObjectQuery and then call its ToTraceString method. Now, things are very different, although I may say, still rather tricky!

private static readonly TypeInfo QueryCompilerTypeInfo = typeof(QueryCompiler).GetTypeInfo();
private static readonly FieldInfo QueryCompilerField = typeof(EntityQueryProvider).GetTypeInfo().DeclaredFields.First(x => x.Name == “_queryCompiler”);
private static readonly PropertyInfo NodeTypeProviderField = QueryCompilerTypeInfo.DeclaredProperties.Single(x => x.Name == “NodeTypeProvider”);
private static readonly MethodInfo CreateQueryParserMethod = QueryCompilerTypeInfo.DeclaredMethods.First(x => x.Name == “CreateQueryParser”);
private static readonly FieldInfo DataBaseField = QueryCompilerTypeInfo.DeclaredFields.Single(x => x.Name == “_database”);
private static readonly FieldInfo QueryCompilationContextFactoryField = typeof(Database).GetTypeInfo().DeclaredFields.Single(x => x.Name == “_queryCompilationContextFactory”);
public static string ToSql(this IQueryable query) where TEntity : class
{
if (!(query is EntityQueryable) && !(query is InternalDbSet))
{
throw new ArgumentException(“Invalid query”);
}
var queryCompiler = (IQueryCompiler) QueryCompilerField.GetValue(query.Provider);
var nodeTypeProvider = (INodeTypeProvider) NodeTypeProviderField.GetValue(queryCompiler);
var parser = (IQueryParser) CreateQueryParserMethod.Invoke(queryCompiler, new object[] { nodeTypeProvider });
var queryModel = parser.GetParsedQuery(query.Expression);
var database = DataBaseField.GetValue(queryCompiler);
var queryCompilationContextFactory = (IQueryCompilationContextFactory)
ueryCompilationContextFactoryField.GetValue(database);
var queryCompilationContext = queryCompilationContextFactory.Create(false);
var modelVisitor = (RelationalQueryModelVisitor) queryCompilationContext.CreateQueryModelVisitor();
modelVisitor.CreateQueryExecutor(queryModel);
var sql = modelVisitor.Queries.First().ToString();
return sql;
}

You can see that it needs some reflection, meaning, things *may* break on a future version. I cached all of the fields to make the access faster in subsequent calls. For the time being, it works perfectly:

var sql1 = ctx.Blogs.ToSql();
var sql2 = ctx
.Blogs
.Where(b => b.CreationDate.Year == 2017)
.ToSql();

Entity Framework Core – Part 5