Dockerfile "COPY" command confusion - docker

Question

I have 3 .NET6 projects in my local 'src' folder as below:
src/A
src/B
src/C
A: web api project, has many nuget dependencies
B: class lib, dependent of A
C: class lib, dependent of A
(Note: of course, project related files including .csproj are present in the local project folders)
My Dockerfile is in project folder A.
I am running the "docker build" command from 'src' folder (i.e. this is the build context) as below:
docker build -f A/Dockerfile -t myapiimage:v1 .
below section of code is from my Dockerfile, where i try to restore nuget dependencies:
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ./A/*.csproj A/
RUN dotnet restore A/A.csproj
this works fine and i understand that .csproj in the image is stored inside /src/A/A.csproj
Am i right?
I want to know whether COPY preserves the source folder structure in the image being built or not?
because after the below 3 lines:
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY *.csproj ./
None of the line works:
RUN dotnet restore A/A.csproj
OR,
RUN dotnet restore A.csproj
OR,
RUN dotnet restore *A.csproj
OR,
RUN dotnet restore src/A/A.csproj
So, where this .csproj files (of all 3 projects) are getting stored in the image?

Answer 1

Your line COPY *.csproj ./ doesn't copy anything, because there are no .csproj files in your src directory on the host machine.
The way I usually do it is a bit clunky. First I do
COPY */*.csproj ./
which copies all the .csproj files into the workdir in the image. Then I do
RUN for file in $(ls *.csproj); do mkdir -p ${file%.*}/ && mv $file ${file%.*}/; done
which looks at all the .csproj files and creates a directory for them and moves them into that directory.
With that approach, your Dockerfile would look like this
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY */*.csproj ./
RUN for file in $(ls *.csproj); do mkdir -p ${file%.*}/ && mv $file ${file%.*}/; done
RUN dotnet restore A/A.csproj