Consuming Npgsql inside PowerShell 5.1

The issue

I am trying to consume the npgsql package with PowerShell 5.1. I tried out three versions:

• 5.0.3
• 4.1.8
• 4.0.11 Only 4.0.11 seems to work.

Steps to reproduce

4.0.11: Add-Type -Path “npgsql.dll” This works.

4.1.8: Add-Type -Path “npgsql.dll” results in add-type : Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more informati on.

try {
Add-Type -Path "npgsql.dll"
}
catch {
$err = $_
}

$err.Exception.LoaderExceptions

yields:

Could not load file or assembly 'System.Threading.Tasks.Extensions, Version=4.2.0.0, Culture=neutral, PublicKeyToken=cc
7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified.

5.0.3: Also yields

Could not load file or assembly 'System.Threading.Tasks.Extensions, Version=4.2.0.0, Culture=neutral, PublicKeyToken=cc
7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified.

I fiddled with additional Add-Type and also provided the -ReferencedAssemblies parameter but to no avail.

Further technical details

Operating system: Windows 10

Other details about my project setup: PowerShell 5.1

[Brar]

Just out of curiosity I tried how Npgsql would work from a current PowerShell and got the following example to run:

# PowerShell 7.1.3 on Windows connecting to a local database using integrated security
New-Item -Name "NpgsqlExample" -ItemType "directory"
Set-Location -Path "NpgsqlExample"
Install-Package -Name Npgsql -ProviderName NuGet -Scope CurrentUser -RequiredVersion 5.0.3 -SkipDependencies -Destination . -Force
$NpgsqlPath = Resolve-Path ".\Npgsql.5.0.3\lib\netstandard2.1\Npgsql.dll"
[System.Reflection.Assembly]::LoadFrom($NpgsqlPath)
try
{
    $conn = [Npgsql.NpgsqlConnection]::new("Host=localhost;Username=$Env:USERNAME;Integrated Security=true")
    $conn.Open()
    $cmd = [Npgsql.NpgsqlCommand]::new("CREATE TABLE data (id integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY, value text NOT NULL)", $conn)
    $cmd.ExecuteNonQuery()
    $cmd.CommandText = "INSERT INTO data (value) VALUES ('First row'), ('Second row'), ('Third row')"
    $cmd.ExecuteNonQuery()
    $cmd.CommandText = "SELECT value FROM data"
    $reader = $cmd.ExecuteReader()
    while($reader.Read())
    {
        Write-Host $reader.GetString(0)
    }
}
finally
{
    if ($null -ne $reader)
    {
        $reader.Dispose()
        $reader = $null
    }
    if ($null -ne $cmd)
    {
        $cmd.Dispose()
        $cmd = $null
    }
    if ($null -ne $conn)
    {
        $conn.Dispose()
        $conn = $null
    }
}

[Brar]

Hi @KrisztianKaszas, my example above also works on PowerShell 5.1.x but you have to be aware of the fact that the “classic” PowerShell versions rely on .NET Framewok (4.5 to be precise). This is why Npgsql 4.0.x is the latest version you can use. Also since Npgsql for .NET framework needs a few NuGet packages to work you have to make sure that they are also available and resolved in the appropriate way. This makes my example a bit longer but it should still work.

# PowerShell 5.1.19041.1682 on Windows connecting to a local database using integrated security
# You may need to install the NuGet package provider via Install-PackageProvider -Name "NuGet"
New-Item -Name "NpgsqlExample" -ItemType "directory"
Set-Location -Path "NpgsqlExample"

Install-Package -Name System.Threading.Tasks.Extensions -ProviderName NuGet -Scope CurrentUser -RequiredVersion 4.5.4 -SkipDependencies -Destination . -Force
Install-Package -Name System.Runtime.CompilerServices.Unsafe -ProviderName NuGet -Scope CurrentUser -RequiredVersion 5.0.0 -SkipDependencies -Destination . -Force
Install-Package -Name System.Memory -ProviderName NuGet -Scope CurrentUser -RequiredVersion 4.5.4 -SkipDependencies -Destination . -Force
Install-Package -Name Npgsql -ProviderName NuGet -Scope CurrentUser -RequiredVersion 4.0.12 -SkipDependencies -Destination . -Force

$npgsqlPath = Resolve-Path ".\Npgsql.4.0.12\lib\net45\Npgsql.dll"
$taskExtensionsPath = Resolve-Path ".\System.Threading.Tasks.Extensions.4.5.4\lib\netstandard1.0\System.Threading.Tasks.Extensions.dll"
$compilerServicesUnsafePath = Resolve-Path ".\System.Runtime.CompilerServices.Unsafe.5.0.0\lib\net45\System.Runtime.CompilerServices.Unsafe.dll"
$systemMemoryPath = Resolve-Path ".\System.Memory.4.5.4\lib\netstandard1.1\System.Memory.dll"

$onAssemblyResolve = [System.ResolveEventHandler] {
param($sender, $e)

Write-Verbose "Resolving '$($e.Name)'"
if ($e.Name -like 'System.Threading.Tasks.Extensions, *') {
    return [System.Reflection.Assembly]::LoadFrom($taskExtensionsPath)
}
elseif ($e.Name -like 'System.Runtime.CompilerServices.Unsafe, *') {
    return [System.Reflection.Assembly]::LoadFrom($compilerServicesUnsafePath)
}
elseif ($e.Name -like 'System.Memory, *') {
    return [System.Reflection.Assembly]::LoadFrom($systemMemoryPath)
}

Write-Verbose "Unable to resolve assembly name '$($e.Name)'"
return $null
}
[System.AppDomain]::CurrentDomain.add_AssemblyResolve($onAssemblyResolve)
[System.Reflection.Assembly]::LoadFrom($npgsqlPath)

try
{
    $conn = [Npgsql.NpgsqlConnection]::new("Host=localhost;Username=$Env:USERNAME;Integrated Security=true")
    $conn.Open()
    $cmd = [Npgsql.NpgsqlCommand]::new("CREATE TABLE data (id integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY, value text NOT NULL)", $conn)
    $cmd.ExecuteNonQuery()
    $cmd.CommandText = "INSERT INTO data (value) VALUES ('First row'), ('Second row'), ('Third row')"
    $cmd.ExecuteNonQuery()
    $cmd.CommandText = "SELECT value FROM data"
    $reader = $cmd.ExecuteReader()
    while($reader.Read())
    {
        Write-Host $reader.GetString(0)
    }
}
finally
{
    if ($null -ne $reader)
    {
        $reader.Dispose()
        $reader = $null
    }
    if ($null -ne $cmd)
    {
        $cmd.Dispose()
        $cmd = $null
    }
    if ($null -ne $conn)
    {
        $conn.Dispose()
        $conn = $null
    }
}

[System.AppDomain]::CurrentDomain.remove_AssemblyResolve($onAssemblyResolve)

Full disclosure: After successfully executing the above code I sometimes run into a StackOverflowException terminating my PowerShell process when I keep executing commands afterwards. I’m not sure if/how it is related as it happens completely independent of my script execution but it is at least a weird coincidence. Edit: It turns out that it was the custom ResolveEventHandler that caused the crashes (executing the script in pwsh which didn’t crash gave me the hint). I’ve updated the script to unregister the handler after the assemblies have been resolved.