Powershell - Appending folder to path

The following Powershell function can be used to append a folder to the path for a user at the command line.

function AppendPath($filePath) {
 $path = [Environment]::GetEnvironmentVariable("Path")
 $path += ";" + $filePath
 [Environment]::SetEnvironmentVariable("Path", $path)
 Write-Host $path 
}

To call this function, just run the Powershell command:

AppendPath "c:\temp"

You can add this file into your $profile file as a function for easy availability. Run . $profile to reload your $profile file. This will append the folder "c:\temp" to your environment variable PATH. To view your environment variable PATH just enter:

echo $env:path

It is not required, but you can also use Chocolatey's refreshenv script to force update the environment variable if it is still not updating.

Regenerating precompiled views in Entity Framework

This article will present a solution to regenerate precompiled views in Entity Framework. Precompiled views can have a dramatic effect on the startup time of your DbContext / ObjectContext, especially the time to execute the first query against the database. First off, the following class can generate these precompiled views:

using System;
using System.Collections.Generic;
using System.Data.Entity.Core.Mapping;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;

namespace PrecompiledViewGenerator
{
    /// <summary>
    /// Capable of generating pre compiled views that EF can use for quicker startup time when application domains starts.
    /// </summary>
    /// <typeparam name="TDbContext"></typeparam>
    /// <param name="dbContext"></param>
    /// <remarks>See https://github.com/ErikEJ/EntityFramework6PowerTools/tree/community/src/PowerTools Github page for the source code of EF Power tools.</remarks>
    /// <returns>A string containing the precompiled views that can be written to file or database for later use to gain optimized startup speeds of EF in application domains.</returns>
    public class EntityFrameworkPrecompiledViewGenerator
    {
        /// <summary>
        /// Generates pre compiled views from a db context. Uses EF Powertools runtime T4 template (.tt file) for precompiled view generation of views for EF 6 ObjectContext for C#.
        /// </summary>
        /// <typeparam name="TDbContext"></typeparam>
        /// <param name="dbContext"></param>
        /// <param name="viewContainerSuffix">The suffix to apply in the generated file containing the precompiled views</param>
        /// <remarks>See https://github.com/ErikEJ/EntityFramework6PowerTools/tree/community/src/PowerTools Github page for the source code of EF Power tools.</remarks>
        /// <returns>A string containing the precompiled views that can be written to file or database for later use to gain optimized startup speeds of EF in application domains.</returns>
        public string GeneratePrecompiledViews<TDbContext>(TDbContext dbContext, string viewContainerSuffix) where TDbContext : IObjectContextAdapter
        {
            if (string.IsNullOrEmpty(viewContainerSuffix))
                throw new ArgumentNullException(nameof(viewContainerSuffix));
            var objectContext = (dbContext as IObjectContextAdapter)?.ObjectContext; 
            if (objectContext == null)
                throw new ArgumentNullException(nameof(dbContext));
            var viewGenerator = new CSharpViewGenerator();
            var mappingCollection = (StorageMappingItemCollection) objectContext.MetadataWorkspace.GetItemCollection(DataSpace.CSSpace);
            if (mappingCollection == null)
                throw new ArgumentNullException(nameof(dbContext));
            var listOfEdmSchemaErrors = new List<EdmSchemaError>();
            var views = mappingCollection.GenerateViews(listOfEdmSchemaErrors);
            listOfEdmSchemaErrors.ForEach(error =>
            {
                if (error.Severity == EdmSchemaErrorSeverity.Error)
                    throw new ArgumentOutOfRangeException($"An error occurred while trying to generate views for {dbContext.GetType().Name}. The error was: {error.ToString()}");
            });
            viewGenerator.ContextTypeName = dbContext.GetType().FullName;
            viewGenerator.MappingHashValue = mappingCollection.ComputeMappingHashValue();
            viewGenerator.ViewContainerSuffix = viewContainerSuffix;
            viewGenerator.Views = views;
            string precompiledViews = viewGenerator.TransformText();
            return precompiledViews;
        }
    }
}

The following runtime text template (.T4) is used to generate the precompiled views:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System.Data.Entity.Infrastructure.MappingViews;

[assembly: DbMappingViewCacheTypeAttribute(
    typeof(<#= ContextTypeName #>),
    typeof(Edm_EntityMappingGeneratedViews.ViewsForBaseEntitySets<#= ContextTypeName #>))]

namespace Edm_EntityMappingGeneratedViews
{
    using System;
    using System.CodeDom.Compiler;
    using System.Data.Entity.Core.Metadata.Edm;

    /// <summary>
    /// Implements a mapping view cache.
    /// </summary>
    [GeneratedCode("Entity Framework 6 Power Tools", "0.9.2.0")]
    internal sealed class ViewsForBaseEntitySets<#= ViewContainerSuffix #> : DbMappingViewCache
    {
        /// <summary>
        /// Gets a hash value computed over the mapping closure.
        /// </summary>
        public override string MappingHashValue
        {
            get { return "<#= MappingHashValue #>"; }
        }

        /// <summary>
        /// Gets a view corresponding to the specified extent.
        /// </summary>
        /// <param name="extent">The extent.</param>
        /// <returns>The mapping view, or null if the extent is not associated with a mapping view.</returns>
        public override DbMappingView GetView(EntitySetBase extent)
        {
            if (extent == null)
            {
                throw new ArgumentNullException("extent");
            }

            var extentName = extent.EntityContainer.Name + "." + extent.Name;
<#
    var index = 0;
    foreach (var view in Views)
    {
#>

            if (extentName == "<#= view.Key.EntityContainer.Name + "." + view.Key.Name #>")
            {
                return GetView<#= index #>();
            }
<#
        index++;
    }
#>

            return null;
        }
<#
    index = 0;
    foreach (var view in Views)
    {
#>

        /// <summary>
        /// Gets the view for <#= view.Key.EntityContainer.Name + "." + view.Key.Name #>.
        /// </summary>
        /// <returns>The mapping view.</returns>
        private static DbMappingView GetView<#= index #>()
        {
            return new DbMappingView(@"<#= view.Value.EntitySql #>");
        }
<#
        index++;
    }
#>
    }
}
<#+
    public string ContextTypeName { get; set; }
 public string ViewContainerSuffix { get; set; }
    public string MappingHashValue { get; set; }
    public dynamic Views { get; set; }
#>

This T4 file is compiled into the class CSharpViewGenerator. Our DbContext can now check the mapping hash value of the loaded precompiled views file in your assembly and compute in again to quickly assert if the database is in sync with the precompiled views. The following code can establish both a check that the precompiled views are in sync and run code that will regenerate the precompiled views file of which the developer can then copy from Notepad and into the precompiled view file again. Not perhaps an elegant solution, but it lets the developer easily check and keep the precompiled views file updated and in sync. And you do not need to install the EF Powertools extension either, as I use the .tt file and much of the source code from there which is part of the "Generate views" command anywyays! Sample DbContext is then:

using System;
using System.Data.Entity;
using System.Data.Entity.Core;
using System.Data.Entity.Core.Mapping;
using System.Data.Entity.Core.Metadata.Edm;
using System.Diagnostics;
using System.IO;
using System.Runtime.CompilerServices;
using Edm_EntityMappingGeneratedViews;

using PrecompiledViewGenerator;

namespace SomeAcme.SomeRegistry.Data
{
    public class SomeDatabaseMigrationsFactory : DatabaseMigrationsFactory<SomeDatabase>
    {
    }

    public class SomeDatabase : SomeDatabaseBaseClass
    {
        public DbSet<SomeEntity> SomeEntity { get; set; }

        public SomeDatabase(ISomeDependency dep)
            : base(dep)
        {
            var someEntityPrecompiledViewsMapping = new ViewsForBaseEntitySetsSomeEntityDatabase();
            var mappingCollection = (StorageMappingItemCollection)ObjectContext.MetadataWorkspace.GetItemCollection(DataSpace.CSSpace);
            string mappingHashValue =  mappingCollection.ComputeMappingHashValue();
            if (SomeEntityPrecompiledViewsMapping.MappingHashValue != mappingHashValue)
            {
                var precompiledViewGenerator = new EntityFrameworkPrecompiledViewGenerator();
                string precompiledViewsContents = precompiledViewGenerator.GeneratePrecompiledViews(this, this.GetType().Name);
                string viewFileForMainDb = "SomeEntityDatabase.Views.cs";
                string temporaryPrecompiledViewFile = Path.Combine(Path.GetTempPath(), viewFileForMainDb);
                try
                {
                    File.WriteAllText(temporaryPrecompiledViewFile, precompiledViewsContents);
                    Process.Start("c:\\windows\\notepad.exe", temporaryPrecompiledViewFile);
                }
                catch (Exception err)
                {
                    throw new Exception("An error occured while trying to regenerate precompiled views for EF since the database changed. Error is: " + err);
                }
                throw new EntityCommandCompilationException($"The precompiled views file is not in sync with the database any longer. Replace the file {viewFileForMainDb} with the generated new contents!");
            }
        }
    }
}

The overall execution of code is the following:

• In the DbContext constructor - check that the computed mapping hash value matches to that of the of the CSSpace storagemapping collection that your precompiled views file contains (MappingHashValue)
• If the hash values do not agree, it is necessary to regenerate the pre compiled views file again. The contents are generated and written to a temporary file.
• Notepad or similar is launched telling the developer to replace the pre compiled views file contents with this new contents.
• An EntityCommandCompilationException is thrown as this is the same type of exception that is thrown if the precompiled views file does not agree
• Developer replaces the contents and rebuilds the solution
• The next time the startup time of EF should be reduced significantly again and work, since our DbContext and precomplied views are in sync again

Below is a sample of an exception thrown when my DbContext was not in sync with the precompiled views file:

System.Data.Entity.Core.EntityCommandCompilationException

System.Data.Entity.Core.EntityCommandCompilationException
  HResult=0x8013193B
  Message=An error occurred while preparing the command definition. See the inner exception for details.
  Source=EntityFramework
  StackTrace:
   at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition..ctor(DbProviderFactory storeProviderFactory, DbCommandTree commandTree, DbInterceptionContext interceptionContext, IDbDependencyResolver resolver, BridgeDataReaderFactory bridgeDataReaderFactory, ColumnMapFactory columnMapFactory)
   at System.Data.Entity.Core.EntityClient.Internal.EntityProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.CreateCommandDefinition(ObjectContext context, DbQueryCommandTree tree)
   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.Prepare(ObjectContext context, DbQueryCommandTree tree, Type elementType, MergeOption mergeOption, Boolean streaming, Span span, IEnumerable`1 compiledQueryParameters, AliasGenerator aliasGenerator)
   at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
   atProgram.cs:line 164

Inner Exception 1:
MappingException: The current model no longer matches the model used to pre-generate the mapping views, as indicated by the ViewsForBaseEntitySetsabf8c33ac61e42fc601fe7446b41eaf48c7577efe6d6e17ccccc2b434793c28e.MappingHashValue property. Pre-generated mapping views must be either regenerated using the current model or removed if mapping views generated at runtime should be used instead. See http://go.microsoft.com/fwlink/?LinkId=318050 for more information on Entity Framework mapping views.

 

Finding databases with biggest tables in SQL Server

I created a T-SQL script today for use with SQL Server that will list the tables that have most rows for SQL Server, able to loop through all databases.

DECLARE @currentDB AS VARCHAR(100)
DECLARE @mrsdb_sqlscript AS NVARCHAR(500)
DECLARE db_cursor CURSOR FOR 
SELECT name from sys.databases where state_desc <> 'offline' and name not in ('master', 'tempdb', 'model', 'msdb') order by name 
DROP TABLE IF EXISTS #largestTables 
CREATE TABLE #largestTables (
 DatabaseName VARCHAR(100),
 SchemaName VARCHAR(200), 
 TableName VARCHAR(200), 
 TotalRowCount INT 
)

OPEN db_cursor 
FETCH NEXT from db_cursor into @currentDB 

WHILE @@FETCH_STATUS = 0 
BEGIN
 SET @mrsdb_sqlscript = N'INSERT INTO #largestTables 
  SELECT ''' + @currentDB + ''' , SCHEMA_NAME(schema_id) AS [SchemaName],
 [Tables].name AS [TableName],
 SUM([Partitions].[rows]) AS [TotalRowCount]
 FROM ' + @currentDB + '.sys.tables AS [Tables]
 JOIN ' + @currentDB + '.sys.partitions AS [Partitions]
 ON [Tables].[object_id] = [Partitions].[object_id]
 AND [Partitions].index_id IN ( 0, 1 )
 GROUP BY SCHEMA_NAME(schema_id), [Tables].name';

 PRINT 'Looking for largest table in the following DB: ' + @currentDB 
 exec sp_executesql @mrsdb_sqlscript 

 FETCH NEXT FROM db_cursor into @currentDB
END

CLOSE db_cursor 
DEALLOCATE db_cursor 

SELECT TOP 100 * FROM #largestTables 
ORDER BY TotalRowCount DESC, Schemaname ASC

The SQL script above will use a temporary table variable and database cursor and loop through all databases, executing a SQL script that will insert data into a temporary table variable and after the cursor has looped through its dataset, the result in the temporary table variable is presented to the DBA monitoring. Use it to spot where you have much data in your databases of the data base server you are working with!