Question

我想使用linq批量删除表中的记录。有一篇帖子描述了如何做到这一点： Bulk-deleting in LINQ to Entities

var query = from c in ctx.Customers
            where c.SalesPerson.Email == "..."
            select c;

query.Delete();

但我的var变量中不存在“删除”功能。
此外，我的上下文中不存在“SubmitChanges”功能。

Answer 1

有一个有趣的NuGet包lets you do batch deletes and updates：

Answer 2

实体框架中目前不支持批量删除。它实际上是在codeplex上讨论的功能之一，现在EF是开源的。

EntityFramework.Extended提供了批量删除支持（你可以在nuget中找到它）但是我的经验是它有一些性能问题。

Answer 3

此代码向任何DbContext添加一个简单的扩展方法，该方法将批量删除您提供的实体框架查询中引用的任何表中的所有数据。它的工作原理是简单地提取查询中涉及的所有表名，并尝试通过发出“DELETE FROM tablename”SQL查询来删除数据，这在大多数类型的数据库中都很常见。

要使用，只需执行以下操作：

myContext.BulkDelete(x => x.Things);

将删除链接到Things实体商店的表格中的所有内容。

代码：

using System.Linq;
using System.Text.RegularExpressions;

namespace System.Data.Entity {

    public static class DbContextExtensions {

        /// <summary>
        /// Efficiently deletes all data from any database tables used by the specified entity framework query. 
        /// </summary>
        /// <typeparam name="TContext">The DbContext Type on which to perform the delete.</typeparam>
        /// <typeparam name="TEntity">The Entity Type to which the query resolves.</typeparam>
        /// <param name="ctx">The DbContext on which to perform the delete.</param>
        /// <param name="deleteQuery">The query that references the tables you want to delete.</param>
        public static void BulkDelete<TContext, TEntity>(this TContext ctx, Func<TContext, IQueryable<TEntity>> deleteQuery) where TContext : DbContext {

            var findTables = new Regex(@"(?:FROM|JOIN)\s+(\[\w+\]\.\[\w+\])\s+AS");
            var qry = deleteQuery(ctx).ToString();

            // Get list of all tables mentioned in the query
            var tables = findTables.Matches(qry).Cast<Match>().Select(m => m.Result("$1")).Distinct().ToList();

            // Loop through all the tables, attempting to delete each one in turn
            var max = 30;
            var exception = (Exception)null;
            while (tables.Any() && max-- > 0) {

                // Get the next table
                var table = tables.First();

                try {
                    // Attempt the delete
                    ctx.Database.ExecuteSqlCommand(string.Format("DELETE FROM {0}", table));

                    // Success, so remove table from the list
                    tables.Remove(table);

                } catch (Exception ex) {
                    // Error, probably due to dependent constraint, save exception for later if needed.                    
                    exception = ex;

                    // Push the table to the back of the queue
                    tables.Remove(table);
                    tables.Add(table);
                }
            }

            // Error error has occurred, and cannot be resolved by deleting in a different 
            // order, then rethrow the exception and give up.
            if (max <= 0 && exception != null) throw exception;

        }
    }
}

Answer 4

我这样做似乎工作得很好。如果有任何理由说这是不好的做法，请告诉我们。

        var customersToDelete = await ctx.Customers.Where(c => c.Email == "...").ToListAsync();

        foreach (var customerToDelete in customersToDelete)
        {
            ctx.Customers.Remove(customerToDelete);
        }

        await ctx.SaveChangesAsync();

Answer 5

在SaveChanges调用之后EF执行数千个DELETE查询时，我遇到了同样的问题。我不确定EntityFramework.Extensions商业库是否会对我有所帮助，所以我决定自己实施批量DELETE并提出类似于BG100's solution的东西！

public async Task<List<TK>> BulkDeleteAsync(List<TK> ids)
{
    if (ids.Count < 1) {
        return new List<TK>();
    }

    // NOTE: DbContext here is a property of Repository Class
    // SOURCE: https://stackoverflow.com/a/9775744
    var tableName = DbContext.GetTableName<T>();
    var sql = $@"
        DELETE FROM {tableName}
        OUTPUT Deleted.Id
        // NOTE: Be aware that 'Id' column naming depends on your project conventions
        WHERE Id IN({string.Join(", ", ids)});
    ";
    return await @this.Database.SqlQuery<TK>(sql).ToListAsync();
}

如果您有类似通用存储库之类的东西应该对您有用。至少您可以尝试使其适合您的EF基础架构。

我还对其进行了一些微调，并且能够对多个实体块执行查询。如果数据库中的查询大小有任何限制，它将为您提供帮助。

const int ChunkSize = 1024;
public async Task<List<TK>> BulkDeleteAsync(List<TK> ids)
{
    if (ids.Count < 1) {
        return new List<TK>();
    }
    // SOURCE: https://stackoverflow.com/a/20953521/11344051
    var chunks = ids.Chunks(ChunkSize).Select(c => c.ToList()).ToList();
    var tableName = DbContext.GetTableName<T>();

    var deletedIds = new List<TK>();
    foreach (var chunk in chunks) {
        var sql = $@"
            DELETE FROM {tableName}
            OUTPUT Deleted.Id
            WHERE Id IN({string.Join(", ", chunk)});
        ";
        deletedIds.AddRange(DbContext.Database.SqlQuery<TK>(sql).ToListAsync());
    }
    return deletedIds;
}

实体框架中的批量删除

5 个答案: