linq-to-entities

问题 With the following table structure (extraneous columns removed) create table [Events] ( ID int not null identity, Name nvarchar(128) not null, constraint PK_Events primary key(ID) ) create table [Donations] ( ID int not null identity, EventID int not null, Amount decimal(10, 2) not null, constraint PK_Donations primary key(ID), constraint FK_Donations_Events foreign key(EventID) references [Events](ID) on update no action on delete no action ) I use the following Linq-to-Entities queries: //

问题 I cannot wrap my head around how i manage to select columns in a queryable by specifying an expression as a parameter. Method A(IQueryable<Order> query) Inside Method A i want to specify which columns to select, so i dont get all columns right away, like this: query.Select(x => new { x.OrderNumber, x.Payment, x.Customer }) This is easy if i specify this directly in Method A, but i want to pass the information using a parameter. I tried using a expression like this: Expression<Func<Order,

问题 My question is two-fold. 1) I am coding a forum and I'm having trouble figuring out how to store time zones for the users of the forum. They will be able to set their time zone and have all dates on the forum modified accordingly. Do I have to create a DB table with timezone names and the number to adjust the server time by? Does .NET have time zone support built in somewhere? 2) Once I've figured out how to store the user's time zone and then modify a DateTime object to the right time, I

问题 I'm not sure if this has been answered yet, I looked at a couple of questions but I don't think they were quite what I was after. Let's say I have 3 tables: Restaurant 1.....M MenuCategory 1.....M MenuItem I have a L2E query that looks something like this: Restaurant = context.Restaurant .Include(r => r.MenuCategory) .FirstOrDefault(r => r.RestaurantId == resaurantId); Which works to some extent, but it only pre-loads the menu categories. As a work around I am able to iterate around each

问题 I'm not sure if this has been answered yet, I looked at a couple of questions but I don't think they were quite what I was after. Let's say I have 3 tables: Restaurant 1.....M MenuCategory 1.....M MenuItem I have a L2E query that looks something like this: Restaurant = context.Restaurant .Include(r => r.MenuCategory) .FirstOrDefault(r => r.RestaurantId == resaurantId); Which works to some extent, but it only pre-loads the menu categories. As a work around I am able to iterate around each

问题 Say I have an entity that I want to query with ranking applied: public class Person: Entity { public int Id { get; protected set; } public string Name { get; set; } public DateTime Birthday { get; set; } } In my query I have the following: Expression<Func<Person, object>> orderBy = x => x.Name; var dbContext = new MyDbContext(); var keyword = "term"; var startsWithResults = dbContext.People .Where(x => x.Name.StartsWith(keyword)) .Select(x => new { Rank = 1, Entity = x, }); var

问题 I have an entity that I'd like to compare with a subset and determine to select all except the subset. So, my query looks like this: Products.Except(ProductsToRemove(), new ProductComparer()) The ProductsToRemove() method returns a List<Product> after it performs a few tasks. So in it's simplest form it's the above. The ProductComparer() class looks like this: public class ProductComparer : IEqualityComparer<Product> { public bool Equals(Product a, Product b) { if (ReferenceEquals(a, b))

问题 I have an entity that I'd like to compare with a subset and determine to select all except the subset. So, my query looks like this: Products.Except(ProductsToRemove(), new ProductComparer()) The ProductsToRemove() method returns a List<Product> after it performs a few tasks. So in it's simplest form it's the above. The ProductComparer() class looks like this: public class ProductComparer : IEqualityComparer<Product> { public bool Equals(Product a, Product b) { if (ReferenceEquals(a, b))

问题 I am using Linq to entities to query the database to get the list of int for further processing. I have two ways to get the list as below: First is: List<int> lstBizIds = new List<int>() { 1, 2, 3, 4, 5 }; List<int> lstProjectIds = context.Projects.Where(x => lstBizIds.Contains(x.businessId)).Select(x => x.projectId).ToList(); Second is: List<int> lstBizIds = new List<int>() { 1, 2, 3, 4, 5 }; List<int> lstProjectIds = context.Projects.Join(lstBizIds, p => p.businessId, u => u, (p, u) => p

问题 Lets say that I have a particular way of deciding whether some strings "match", like this: public bool stringsMatch(string searchFor, string searchIn) { if (string.IsNullOrEmpty(searchFor)) { return true; } return searchIn != null && (searchIn.Trim().ToLower().StartsWith(searchFor.Trim().ToLower()) || searchIn.Contains(" " + searchFor)); } I would like to pull matches out of a database using Linq To Entities and this helper. However, when I try this: IQueryable<Blah> blahs = query.Where(b =>