Render ERD — render_erd • ERDbuilder

The render_erd function graphically renders ERD using DiagrammeR, incorporating pseudo-nodes to depict traditional ERD notations such as cardinality. This function uses edge attributes to append text labels near the end of the edge lines. Specifically, the DiagrammeR label attribute is leveraged to include text labels at the ends of the edges, which effectively convey the intended cardinality and relationship information. This function constructs edge labels from two strings representing the left and right relationship attributes.

Usage

render_erd(erd_object, label_distance = 2.5, label_angle = 45, n = 10)

Arguments

erd_object: An object of class "ERD", generated using the link{create_erd} function. This object encapsulates the data frames representing the entities and the relationships between these entities.
label_distance: A numeric value that specifies the distance between the edge labels and the lines connecting the nodes. The default value is 2.5.
label_angle: A numeric value that specifies the angle at which the edge labels are displayed. The default value is 45 degrees.
n: The maximum number of rows in each table. The tables will add columns to show all of the variables in the tables such that there are only `n` rows.

Value

A DiagrammeR graph object representing the ERD.

Details

This function is responsible for graphically rendering an Entity-Relationship Diagram (ERD) based on an object of class "ERD". This function leverages the DiagrammeR package to generate a graph that visually represents both the entities and the relationships contained within the ERD object. The entities are represented as nodes, and the relationships as edges. The render_erd function thus provides a robust mechanism for visually representing an ERD based on structured data within the R environment. By converting an ERD object into a graphical form, the function aids in a clearer understanding and communication of complex data relationships.

Nodes: Each entity (i.e., data frame) is represented as a node. The node label consists of the entity name and the attribute names within the entity.

Edges: Relationships between entities are represented as edges between the corresponding nodes. Labels at the ends of the edges indicate the type and cardinality of the relationship.

The label_distance and label_angle parameters control the presentation of edge labels in the ERD to minimize overlap and improve readability.

The function uses a for loop to iterate through the entities and relationships, constructing the necessary DiagrammeR code to render each element. The nodesep and ranksep parameters in the DiagrammeR code control the node spacing in the rendered ERD, making it easier to visualize complex ERDs.

Examples



# Load Packages -----------------------------------------------------------

library(ERDbuilder)
library(dplyr)

# Define entities ---------------------------------------------------------

students_tbl <- data.frame(
  st_id = c("hu1", "de2", "lo3"),
  dep_id = c("water", "evil", "values"),
  student = c("Huey", "Dewey", "Louie"),
  email = c("hubert.duck", "dewfort.duck", "llewellyn.duck"),
  dob = c("04-15", "04-15", "04-15")
)

courses_tbl <- data.frame(
  crs_id = c("water101", "evil205", "water202"),
  fac_id = c("02do", "03pe", "04mi"),
  dep_id = c("water", "evil", "water"),
  course = c("Swimming", "Human-chasing", "Dives")
)

enrollment_tbl <- data.frame(
  crs_id = c("water101", "evil205", "evil205", "water202"),
  st_id = c("hu1", "hu1", "de2", "de2"),
  final_grade = c("B", "A", "A", "F")
)

department_tbl <- data.frame(
  dep_id = c("water", "evil", "values"),
  department = c("Water activities", "Evil procurement", "Good values")
)

faculty_tbl <- data.frame(
  faculty_name = c("Scrooge McDuck", "Donald", "Pete", "Mickey"),
  title = c("Emeritus", "Full", "Assistant", "Full"),
  fac_id = c("01sc", "02do", "03pe", "04mi"),
  dep_id = c("water", "water", "evil", "values")
)

head(students_tbl)
#>   st_id dep_id student          email   dob
#> 1   hu1  water    Huey    hubert.duck 04-15
#> 2   de2   evil   Dewey   dewfort.duck 04-15
#> 3   lo3 values   Louie llewellyn.duck 04-15
head(courses_tbl)
#>     crs_id fac_id dep_id        course
#> 1 water101   02do  water      Swimming
#> 2  evil205   03pe   evil Human-chasing
#> 3 water202   04mi  water         Dives
head(enrollment_tbl)
#>     crs_id st_id final_grade
#> 1 water101   hu1           B
#> 2  evil205   hu1           A
#> 3  evil205   de2           A
#> 4 water202   de2           F
head(department_tbl)
#>   dep_id       department
#> 1  water Water activities
#> 2   evil Evil procurement
#> 3 values      Good values
head(faculty_tbl)
#>     faculty_name     title fac_id dep_id
#> 1 Scrooge McDuck  Emeritus   01sc  water
#> 2         Donald      Full   02do  water
#> 3           Pete Assistant   03pe   evil
#> 4         Mickey      Full   04mi values

## Define relationships----------------------------------------
relationships <- list(
  courses = list(
    enrollment = list(crs_id = "crs_id", relationship = c("||", "|<")),
    department = list(dep_id = "dep_id", relationship = c(">|", "||")),
    faculty = list(fac_id = "fac_id", relationship = c(">0", "||"))
  ),
  enrollment = list(
    students = list(st_id = "st_id", relationship = c(">0", "||")
    )
  ),
  students = list(
    department = list(dep_id = "dep_id", relationship = c(">|", "||"))
  ),
  faculty = list(
    department = list(dep_id = "dep_id", relationship = c(">|", "||"))
  )
)

## Create ERD object
erd_object <-
  create_erd(
    list(
      students = students_tbl,
      courses = courses_tbl,
      enrollment = enrollment_tbl,
      department = department_tbl,
      faculty = faculty_tbl
    ),
    relationships)

## Render ERD -----------------------------------------------------------
render_erd(erd_object, label_distance = 0, label_angle = 15, n = 20)