Net笔记-EF/EF Core/Dapper等ORM开发记录

 个人备查笔记

 

 

Q.EF Core 视图的模型映射：

　　Note：EF的CreateDbDatabase和数据迁移并不会自动创建视图，需要手动创建...

　　简单例子：

　　配置类：

    public class View_AccountFemaleEFConfig : IEntityTypeConfiguration<View_AccountFemale>
    {
        public void Configure(EntityTypeBuilder<View_AccountFemale> builder)
        {
            #region //水平拆分处理处
            builder.ToView<View_AccountFemale>("View_AccountFemale").SetupBaseEntity();
            #endregion
        }
    }

  　　上下文：

 public class ExamContext : DbContext
    {
        virtual public DbSet<View_AccountFemale> view_AccountFemales { get; }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            // Database 必须存在 View_AccountFemale 视图，否则将报错
            modelBuilder.ApplyConfiguration<View_AccountFemale>(new View_AccountFemaleEFConfig());

            base.OnModelCreating(modelBuilder);
        }

 

Q:EF DateTime 默认值多数据兼容问题：

mysql:NOW()或sysdate()

Sql Server: GetDate()

EF兼容使用 ANSI SQL:

builder.Property(x => x.UpdatedOn).HasDefaultValueSql("CURRENT_TIMESTAMP");

 

 

Q:EF/Linq语句转Raw SQL：

代码转载备查,

 

转载来源：https://stackoverflow.com/questions/37527783/get-sql-code-from-an-entity-framework-core-iqueryablet

 

EF Core 2.x:

    public static class QueryableExtensions
    {
        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 FieldInfo QueryModelGeneratorField = typeof(QueryCompiler).GetTypeInfo().DeclaredFields.First(x => x.Name == "_queryModelGenerator"); private static readonly FieldInfo DataBaseField = QueryCompilerTypeInfo.DeclaredFields.Single(x => x.Name == "_database"); private static readonly PropertyInfo DatabaseDependenciesField = typeof(Database).GetTypeInfo().DeclaredProperties.Single(x => x.Name == "Dependencies"); public static string ToSql<TEntity>(this IQueryable<TEntity> query) { var queryCompiler = (QueryCompiler) QueryCompilerField.GetValue(query.Provider); var queryModelGenerator = (QueryModelGenerator)QueryModelGeneratorField.GetValue(queryCompiler); var queryModel = queryModelGenerator.ParseQuery(query.Expression); var database = DataBaseField.GetValue(queryCompiler); var databaseDependencies = (DatabaseDependencies) DatabaseDependenciesField.GetValue(database); var queryCompilationContext = databaseDependencies.QueryCompilationContextFactory.Create(false); var modelVisitor = (RelationalQueryModelVisitor) queryCompilationContext.CreateQueryModelVisitor(); modelVisitor.CreateQueryExecutor<TEntity>(queryModel); var sql = modelVisitor.Queries.First().ToString(); return sql; } }

 

EF Core 3.x:

        public static string ToSql<T>(this IQueryable<T> query)
        {
            var enumerator = query.Provider.Execute<IEnumerable<T>>(query.Expression).GetEnumerator(); var enumeratorType = enumerator.GetType(); var selectFieldInfo = enumeratorType.GetField("_selectExpression", BindingFlags.NonPublic | BindingFlags.Instance) ?? throw new InvalidOperationException($"cannot find field _selectExpression on type {enumeratorType.Name}"); var sqlGeneratorFieldInfo = enumeratorType.GetField("_querySqlGeneratorFactory", BindingFlags.NonPublic | BindingFlags.Instance) ?? throw new InvalidOperationException($"cannot find field _querySqlGeneratorFactory on type {enumeratorType.Name}"); var selectExpression = selectFieldInfo.GetValue(enumerator) as SelectExpression ?? throw new InvalidOperationException($"could not get SelectExpression"); var factory = sqlGeneratorFieldInfo.GetValue(enumerator) as IQuerySqlGeneratorFactory ?? throw new InvalidOperationException($"could not get IQuerySqlGeneratorFactory"); var sqlGenerator = factory.Create(); var command = sqlGenerator.GetCommand(selectExpression); var sql = command.CommandText; return sql; }

 

 

Q:EF的Mysql乐观锁实现：

　　RowVersion只支持Sql Server，如果需要通用（多数据库支持）的乐观锁的话：

　　以EF Core 为例：

　　Entity:

    abstract public class BaseEntity
    {
        public Int64 Qing_Version { get; set; } }

Config：

    public class AccountEFConfig : IEntityTypeConfiguration<Account>
    {
        public void Configure(EntityTypeBuilder<Account> builder) { EntityTypeBuilder<Account> tableBuilder = builder.ToTable("Account"); tableBuilder.Property(x => x.Qing_Version).IsConcurrencyToken(true); } }

重载重写SaveChange/SaveChangeAsyc：

    public class BaseDBContext<DBCtx> : DbContext where DBCtx : DbContext
    {
        public override int SaveChanges() { var validationErrors = this.ChangeTracker; if (this.ChangeTracker != null) { var entities = this.ChangeTracker .Entries() .Where( x => x.State == EntityState.Modified && x.Entity != null && typeof(BaseEntity).IsAssignableFrom(x.Entity.GetType()) ) .Select(x => x) .ToList(); foreach (var entity in entities) { BaseEntity entityBase = entity.Entity as BaseEntity; entityBase.Qing_UpdateTime = DateTime.Now; entityBase.Qing_Version++; } } return base.SaveChanges(); } }

 

 

扩展阅读：

　　但当如果需要做通用的乐观锁支持的话，EF6.x或以上时，需要支持MySQL 的话你需要：

　　https://stackoverflow.com/questions/7608619/optimistic-concurrency-with-entity-framework-and-mysql

　　或

　　https://www.cnblogs.com/easygame/p/4456965.html

　　

　　EF Core 1.x或以上，需要：

　　参考 ：https://long2know.com/2016/07/porting-ef6-to-ef7-or-ef-core/ 

　　实现：  https://stackoverflow.com/questions/40394577/better-way-to-implement-a-row-version-with-ef-core-and-mysql

 　　扩展阅读: https://www.learnentityframeworkcore.com/concurrency