Download E-books Programming Entity Framework: DbContext PDF

By Julia Lerman, Rowan Miller

In addition to Code First, EF 4.1 introduces less complicated EF coding styles with the DbContext, DbSet, ChangeTracker and Validation APIs. This moment mini-book will take the reader on a journey of those new positive factors and the way to exploit them. those new periods and APIs permit the person concentrate on the commonest coding projects with Entity Framework and streamlines entry to styles that are usually used, yet have been formerly non-intuitive and intricate to code. The Validation API that includes DbContext leverages the prevailing .NET four IValidatableObject and ValidationAttributes in addition to supplying extra validation positive factors. you'll study the fine details of having the main from server part validation from the DbContext.

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Five to one hundred fifty miles could be legitimate: [Range(. 5,150)] public decimal MilesFromNearestAirport { get; set; } when you run the applying back, you’ll see this message within the console window: keep Failed: the sector MilesFromNearestAirport has to be among zero. five and one hundred fifty. There’s no point out of the duplication. That’s as the ValidateEntity strategy is designed to envision the valuables and sort ideas first and go back the exception right now if any are found—before it has referred to as ValidateLodging. Let’s go back to the ValidateEntity procedure and strength it to come the mix of validation mistakes checked within the customized common sense and within the good judgment payment via base. ValidateEntity, as visualized in determine 7-3. determine 7-3. Combining mistakes from customized and base validation instance 7-7 demonstrates code that might let you acquire the result of the bottom validation after which upload any extra mistakes present in the customized good judgment to that end result prior to returning the mixed error from ValidateEntity. instance 7-7. Combing style and estate validation effects with context effects safe override DbEntityValidationResult ValidateEntity (DbEntityEntry entityEntry, IDictionary goods) { var consequence = base. ValidateEntity(entityEntry, items); ValidateLodging(result); go back end result; } working the CreateDuplicateLodging approach one final time will now reveal either blunders: keep Failed: the sphere MilesFromNearestAirport has to be among zero. five and a hundred and fifty. there's already a accommodation named Grand inn at this vacation spot. * * * be aware you could comprise a number of validation exams in ValidateEntity. those examples in simple terms include separately for the sake of brevity. * * * Now that you’ve visible a couple of attainable workflows for executing validations in ValidateEntity, you could mimic those or outline your personal workflow while customizing ValidateEntity. * * * extra Refactoring As you enforce this tradition good judgment into your individual software, you've gotten many customized validations outlined on your DbContext type. instead of having to name ValidateReservation, ValidateLodging, and any others from ValidateEntity, you'll mix them right into a unmarried strategy akin to IsValid and get in touch with that from ValidateEntity in its place. for instance: deepest void IsValid(DbEntityValidationResult consequence) { ValidateLodging(result); ValidateReservation(result); } * * * Updating info in the course of SaveChanges ordinarily, there are last-minute adjustments that you really want to make to information ahead of it’s despatched to the database. One instance is surroundings DateAdded and DateModified values on your sessions. whereas there are many how you can accomplish that in . internet code, you'll desire to practice this common sense within the information layer. as the context is already iterating via all of its further and transformed entities while it calls ValidateEntity, it’s tempting so as to add this common sense into ValidateEntity instead of practice an extra enumeration within the SaveChanges technique. It’s attainable to do that, however it isn't really urged. the next are a few downsides to placing this kind of common sense within ValidateEntity: The ValidateEntity procedure is designed for acting validations.

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