Executing query until there is nothing more left
up vote
2
down vote
favorite
I often query a database to get a batch of items to procees. I do this as long as the query returns some items. I use this pattern quite a lot so I thought I create a small helper so that I don't have to implement this logic again and again.
It's a small class that executes the query until there is nothing more left:
public static class Unfold
{
public static async Task ForEachAsync<T>
(
Func<CancellationToken, Task<IList<T>>> query,
Func<IList<T>, CancellationToken, Task> body,
CancellationToken cancellationToken
)
{
while (true)
{
var result = await query(cancellationToken);
if (result.Any())
{
await body(result, cancellationToken);
}
else
{
break;
}
}
}
}
The reason why I implemented it exactly this way is:
- all my queries are
async
- they must always return
IList<T>(if they return a collection of course) - I always process a batch at a time that I then mark as processed
Example
The typical use-case is like this:
- get a batch of items from a repository
- process this batch
- repeat until the batch is empty
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
A test repository:
public class NumberRepository
{
private readonly IList<IList<int>> _numbers = new { new { 1, 2 }, new { 3, 4 }, new { 5 }, new int[0] };
private int _batchIndex;
public Task<IList<int>> GetNumbersAsync(CancellationToken cancellationToken) => Task.FromResult(_numbers[_batchIndex++]);
}
and the processing method:
private Task ProcessBatch<T>(T item, CancellationToken cancellationToken)
{
item.Dump();
return Task.CompletedTask;
}
What do you say? Is this a good or a bad solution? Is there anything missing (but null-checks)?
c# async-await
asked Dec 6 at 10:01
t3chb0t
33.8k746110
add a comment |
up vote
2
down vote
favorite
I often query a database to get a batch of items to procees. I do this as long as the query returns some items. I use this pattern quite a lot so I thought I create a small helper so that I don't have to implement this logic again and again.
It's a small class that executes the query until there is nothing more left:
public static class Unfold
{
public static async Task ForEachAsync<T>
(
Func<CancellationToken, Task<IList<T>>> query,
Func<IList<T>, CancellationToken, Task> body,
CancellationToken cancellationToken
)
{
while (true)
{
var result = await query(cancellationToken);
if (result.Any())
{
await body(result, cancellationToken);
}
else
{
break;
}
}
}
}
The reason why I implemented it exactly this way is:
- all my queries are
async
- they must always return
IList<T>(if they return a collection of course) - I always process a batch at a time that I then mark as processed
Example
The typical use-case is like this:
- get a batch of items from a repository
- process this batch
- repeat until the batch is empty
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
A test repository:
public class NumberRepository
{
private readonly IList<IList<int>> _numbers = new { new { 1, 2 }, new { 3, 4 }, new { 5 }, new int[0] };
private int _batchIndex;
public Task<IList<int>> GetNumbersAsync(CancellationToken cancellationToken) => Task.FromResult(_numbers[_batchIndex++]);
}
and the processing method:
private Task ProcessBatch<T>(T item, CancellationToken cancellationToken)
{
item.Dump();
return Task.CompletedTask;
}
What do you say? Is this a good or a bad solution? Is there anything missing (but null-checks)?
c# async-await
asked Dec 6 at 10:01
t3chb0t
33.8k746110
Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25
add a comment |
up vote
2
down vote
favorite
up vote
2
down vote
favorite
I often query a database to get a batch of items to procees. I do this as long as the query returns some items. I use this pattern quite a lot so I thought I create a small helper so that I don't have to implement this logic again and again.
It's a small class that executes the query until there is nothing more left:
public static class Unfold
{
public static async Task ForEachAsync<T>
(
Func<CancellationToken, Task<IList<T>>> query,
Func<IList<T>, CancellationToken, Task> body,
CancellationToken cancellationToken
)
{
while (true)
{
var result = await query(cancellationToken);
if (result.Any())
{
await body(result, cancellationToken);
}
else
{
break;
}
}
}
}
The reason why I implemented it exactly this way is:
- all my queries are
async
- they must always return
IList<T>(if they return a collection of course) - I always process a batch at a time that I then mark as processed
Example
The typical use-case is like this:
- get a batch of items from a repository
- process this batch
- repeat until the batch is empty
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
A test repository:
public class NumberRepository
{
private readonly IList<IList<int>> _numbers = new { new { 1, 2 }, new { 3, 4 }, new { 5 }, new int[0] };
private int _batchIndex;
public Task<IList<int>> GetNumbersAsync(CancellationToken cancellationToken) => Task.FromResult(_numbers[_batchIndex++]);
}
and the processing method:
private Task ProcessBatch<T>(T item, CancellationToken cancellationToken)
{
item.Dump();
return Task.CompletedTask;
}
What do you say? Is this a good or a bad solution? Is there anything missing (but null-checks)?
c# async-await
asked Dec 6 at 10:01
t3chb0t
33.8k746110
I often query a database to get a batch of items to procees. I do this as long as the query returns some items. I use this pattern quite a lot so I thought I create a small helper so that I don't have to implement this logic again and again.
It's a small class that executes the query until there is nothing more left:
public static class Unfold
{
public static async Task ForEachAsync<T>
(
Func<CancellationToken, Task<IList<T>>> query,
Func<IList<T>, CancellationToken, Task> body,
CancellationToken cancellationToken
)
{
while (true)
{
var result = await query(cancellationToken);
if (result.Any())
{
await body(result, cancellationToken);
}
else
{
break;
}
}
}
}
The reason why I implemented it exactly this way is:
- all my queries are
async
- they must always return
IList<T>(if they return a collection of course) - I always process a batch at a time that I then mark as processed
Example
The typical use-case is like this:
- get a batch of items from a repository
- process this batch
- repeat until the batch is empty
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
A test repository:
public class NumberRepository
{
private readonly IList<IList<int>> _numbers = new { new { 1, 2 }, new { 3, 4 }, new { 5 }, new int[0] };
private int _batchIndex;
public Task<IList<int>> GetNumbersAsync(CancellationToken cancellationToken) => Task.FromResult(_numbers[_batchIndex++]);
}
and the processing method:
private Task ProcessBatch<T>(T item, CancellationToken cancellationToken)
{
item.Dump();
return Task.CompletedTask;
}
What do you say? Is this a good or a bad solution? Is there anything missing (but null-checks)?
c# async-await
c# async-await
asked Dec 6 at 10:01
t3chb0t
33.8k746110
asked Dec 6 at 10:01
t3chb0t
33.8k746110
edited Dec 6 at 11:38
asked Dec 6 at 10:01
t3chb0t
33.8k746110
asked Dec 6 at 10:01
t3chb0t
33.8k746110
asked Dec 6 at 10:01
t3chb0t
33.8k746110
33.8k746110
Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25
add a comment |
Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25
Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25
Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25
add a comment |
1 Answer
1
active
oldest
votes
up vote
3
down vote
accepted
Sorry, but you definitely need a null check here:
if (result.Any())
Else there is not much to comment.
About the usage:
I don't understand, why you create a lambda for the query argument:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
Why not just:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: numbers.GetNumbersAsync,
body: ProcessBatch,
CancellationToken.None
);
}
numbers.GetNumbersAsync is awaitable already?
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
1
Right, and even to avoid thenullcheck at all I definitely need to put the[NotNull]attribute there as I always guaratee that collections are nevernull; Unfortunatelly it does not work well withTask<T>:-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)
– t3chb0t
Dec 6 at 12:36
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
Oh, cool, I didn't know that but one can use the[ItemNotNull]onTask<T>, see - if you're using them too.
– t3chb0t
Dec 6 at 12:47
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
Sorry, but you definitely need a null check here:
if (result.Any())
Else there is not much to comment.
About the usage:
I don't understand, why you create a lambda for the query argument:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
Why not just:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: numbers.GetNumbersAsync,
body: ProcessBatch,
CancellationToken.None
);
}
numbers.GetNumbersAsync is awaitable already?
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
1
Right, and even to avoid thenullcheck at all I definitely need to put the[NotNull]attribute there as I always guaratee that collections are nevernull; Unfortunatelly it does not work well withTask<T>:-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)
– t3chb0t
Dec 6 at 12:36
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
Oh, cool, I didn't know that but one can use the[ItemNotNull]onTask<T>, see - if you're using them too.
– t3chb0t
Dec 6 at 12:47
add a comment |
up vote
3
down vote
accepted
Sorry, but you definitely need a null check here:
if (result.Any())
Else there is not much to comment.
About the usage:
I don't understand, why you create a lambda for the query argument:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
Why not just:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: numbers.GetNumbersAsync,
body: ProcessBatch,
CancellationToken.None
);
}
numbers.GetNumbersAsync is awaitable already?
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
1
Right, and even to avoid thenullcheck at all I definitely need to put the[NotNull]attribute there as I always guaratee that collections are nevernull; Unfortunatelly it does not work well withTask<T>:-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)
– t3chb0t
Dec 6 at 12:36
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
Oh, cool, I didn't know that but one can use the[ItemNotNull]onTask<T>, see - if you're using them too.
– t3chb0t
Dec 6 at 12:47
add a comment |
up vote
3
down vote
accepted
up vote
3
down vote
accepted
Sorry, but you definitely need a null check here:
if (result.Any())
Else there is not much to comment.
About the usage:
I don't understand, why you create a lambda for the query argument:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
Why not just:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: numbers.GetNumbersAsync,
body: ProcessBatch,
CancellationToken.None
);
}
numbers.GetNumbersAsync is awaitable already?
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
Sorry, but you definitely need a null check here:
if (result.Any())
Else there is not much to comment.
About the usage:
I don't understand, why you create a lambda for the query argument:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: async token => await numbers.GetNumbersAsync(token),
body: ProcessBatch,
CancellationToken.None
);
}
Why not just:
async Task Main()
{
var numbers = new NumberRepository();
await Unfold.ForEachAsync
(
query: numbers.GetNumbersAsync,
body: ProcessBatch,
CancellationToken.None
);
}
numbers.GetNumbersAsync is awaitable already?
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
answered Dec 6 at 12:30
Henrik Hansen
6,7081824
6,7081824
1
Right, and even to avoid thenullcheck at all I definitely need to put the[NotNull]attribute there as I always guaratee that collections are nevernull; Unfortunatelly it does not work well withTask<T>:-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)
– t3chb0t
Dec 6 at 12:36
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
Oh, cool, I didn't know that but one can use the[ItemNotNull]onTask<T>, see - if you're using them too.
– t3chb0t
Dec 6 at 12:47
add a comment |
1
Right, and even to avoid thenullcheck at all I definitely need to put the[NotNull]attribute there as I always guaratee that collections are nevernull; Unfortunatelly it does not work well withTask<T>:-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)
– t3chb0t
Dec 6 at 12:36
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
Oh, cool, I didn't know that but one can use the[ItemNotNull]onTask<T>, see - if you're using them too.
– t3chb0t
Dec 6 at 12:47
1
1
Right, and even to avoid the
null check at all I definitely need to put the [NotNull] attribute there as I always guaratee that collections are never null; Unfortunatelly it does not work well with Task<T> :-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)– t3chb0t
Dec 6 at 12:36
Right, and even to avoid the
null check at all I definitely need to put the [NotNull] attribute there as I always guaratee that collections are never null; Unfortunatelly it does not work well with Task<T> :-( In this example using a lambda is not necessary, true, but in my application I have some EF queries there so I wanted to simulate it as real as possible ;-)– t3chb0t
Dec 6 at 12:36
1
1
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
My first try was with observables but I failed to generate them ;-]
– t3chb0t
Dec 6 at 12:38
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
@t3chb0t: Ah, yes, I remember those things :-). But this one is simple and easy to use.
– Henrik Hansen
Dec 6 at 12:44
1
1
Oh, cool, I didn't know that but one can use the
[ItemNotNull] on Task<T>, see - if you're using them too.– t3chb0t
Dec 6 at 12:47
Oh, cool, I didn't know that but one can use the
[ItemNotNull] on Task<T>, see - if you're using them too.– t3chb0t
Dec 6 at 12:47
add a comment |
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Oh, I see some has donvoted it... how so?
– t3chb0t
Dec 8 at 16:25