Querying Data in a System-Versioned Temporal Table in Entity Framework Core

Querying Data in a System-Versioned Temporal Table in Entity Framework Core

To query data in a system-versioned temporal table in Entity Framework Core, you can use LINQ queries with the FromSqlInterpolated method to execute a SQL query against the table. The FromSqlInterpolated method allows you to use interpolated strings to construct a SQL query that includes parameters, which are automatically parameterized to protect against SQL injection attacks.

Here's an example of how you can query a system-versioned temporal table called MyTable with a temporal context called MyContext in Entity Framework Core:

using Microsoft.EntityFrameworkCore; // Define the temporal query parameters var startTime = DateTime.UtcNow.AddDays(-1); var endTime = DateTime.UtcNow; // Execute a temporal query against the MyTable temporal table var query = $@" SELECT * FROM MyTable FOR SYSTEM_TIME BETWEEN {startTime} AND {endTime}"; using (var context = new MyContext()) { var results = await context.MyTable.FromSqlInterpolated(query).ToListAsync(); // Do something with the results }

In this example, the MyTable table is queried using a SQL query that selects all rows with a system time between startTime and endTime. The query is executed using the FromSqlInterpolated method with the MyContext DbContext. The results are returned as a list of MyTable entities.

Examples

  1. "Entity Framework Core query to retrieve all records from a temporal table"

    • Description: Learn how to query all records, including historical versions, from a system-versioned temporal table in Entity Framework Core.
    • Code:
      var allRecords = context.TemporalTable.ToList();

  2. "Entity Framework Core query to filter records based on a specific time range"

    • Description: Understand how to query records from a temporal table within a specified time range in Entity Framework Core.
    • Code:
      var startDate = DateTime.Parse("2022-01-01"); var endDate = DateTime.Parse("2022-12-31"); var filteredRecords = context.TemporalTable .Where(r => r.ValidFrom >= startDate && r.ValidTo <= endDate) .ToList();

  3. "Entity Framework Core query to retrieve the current version of a record"

    • Description: Learn how to query the current version of a record from a temporal table in Entity Framework Core.
    • Code:
      var currentRecord = context.TemporalTable .AsOf(DateTime.Now) .SingleOrDefault(r => r.Id == targetId);

  4. "Entity Framework Core query to retrieve historical versions of a record"

    • Description: Explore how to query historical versions of a record from a temporal table in Entity Framework Core.
    • Code:
      var historicalVersions = context.TemporalTable .AsOf(DateTime.Now.AddMonths(-6)) .Where(r => r.Id == targetId) .ToList();

  5. "Entity Framework Core query to track changes for a specific record"

    • Description: Understand how to query changes made to a specific record in a temporal table over time using Entity Framework Core.
    • Code:
      var changes = context.TemporalTable .AsTracking() .Where(r => r.Id == targetId) .ToList();

  6. "Entity Framework Core query to group temporal records by a specific property"

    • Description: Learn how to use Entity Framework Core to group records from a temporal table based on a specific property.
    • Code:
      var groupedRecords = context.TemporalTable .GroupBy(r => r.Category) .Select(group => new { Category = group.Key, Records = group.ToList() }) .ToList();

  7. "Entity Framework Core query to order temporal records by validity period"

    • Description: Explore how to query temporal records from a table in Entity Framework Core and order them based on their validity period.
    • Code:
      var orderedRecords = context.TemporalTable .OrderBy(r => r.ValidFrom) .ThenBy(r => r.ValidTo) .ToList();

  8. "Entity Framework Core query to count the total number of records in a temporal table"

    • Description: Learn how to count the total number of records, including historical versions, in a system-versioned temporal table using Entity Framework Core.
    • Code:
      var recordCount = context.TemporalTable.Count();

  9. "Entity Framework Core query to retrieve the earliest version of a record"

    • Description: Understand how to query the earliest version of a record from a temporal table in Entity Framework Core.
    • Code:
      var earliestRecord = context.TemporalTable .OrderBy(r => r.ValidFrom) .FirstOrDefault(r => r.Id == targetId);

  10. "Entity Framework Core query to filter records based on a property and time range"

    • Description: Explore how to query records from a temporal table based on a specific property and within a specified time range using Entity Framework Core.
    • Code:
      var startDate = DateTime.Parse("2022-01-01"); var endDate = DateTime.Parse("2022-12-31"); var filteredRecords = context.TemporalTable .Where(r => r.ValidFrom >= startDate && r.ValidTo <= endDate && r.Category == "TargetCategory") .ToList();

More Tags

gravity elasticsearch-aggregation azure-redis-cache vbscript httpd.conf reload facebook-prophet mod-rewrite dialect bitwise-operators

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